Process evaluation of a school-based sexual health intervention targeting 13–14-year-olds in Finland

Young people are particularly vulnerable to challenges that disadvantage their sexual health (Slater and Robinson, 2014). To address these challenges, comprehensive sexuality education (CSE) plays an essential role (Council of Europe, 2020), ensuring adolescents' safe and responsible sexual development (World Health Organization, 2021). Importantly, involving adolescents in the planning, implementation, and evaluation of sexual health programs has been shown to enhance their effectiveness. (Aceves-Martins et al., 2019; World Health Organization, 2025).

Formal learning typically occurs in structured educational settings such as schools, universities, and other educational and training institutions (Johnson and Majewska, 2022), with formal sexuality education most often delivered in schools (Breuner et al., 2016; Lindberg et al., 2016). In Finland, CSE is compulsory and integrated into health education for students in grades 7–9, while for younger pupils in grades 1–6, sexuality education is mainly taught within the subject of environmental science (Finnish National Agency for Education, 2014). Although Finnish sexuality education is often regarded as progressive, it still presents certain shortcomings. For example, implementation is not always systematic, content tends to reflect heteronormative assumptions (Lehtonen et al., 2024), and multicultural perspectives are often lacking (Honkasalo, 2018). Moreover, adolescents are seldom involved in shaping sexuality education or contributing their perspectives. (Honkasalo, 2018; Rinkinen, 2012).

CSE has been shown to yield several favourable health outcomes (Kim et al., 2023). It provides children and adolescents with unbiased, scientifically relevant information about all aspects of sexuality, while also helping them develop the skills needed to act on this information. Furthermore, CSE contributes to the development of responsible and open-minded attitudes (UNESCO et al., 2018).

In addition to curriculum-based education, school-based sexual health interventions can further enhance learning by providing additional resources and fostering engagement (Centers for Disease Control and Prevention, 2025; Myat et al., 2024). While these interventions aim to improve sexual health and well-being (Fenton, 2001; Shahsavari et al., 2020), they are complex due to their sensitive nature and the need for adaptability to regional culture and context. Consequently, their design, implementation, and evaluation require a systematic approach (Bartholomew and Mullen, 2011; Hoffmann et al., 2014).

Although defined in diverse ways (Getachew-Smith et al., 2022), process evaluation generally refers to assessing the extent to which an intervention is implemented as planned (Fraze et al., 2009; Glasgow and Linnan, 2008). This involves examining intervention activities, target audience responsiveness, and exposure (Fraze et al., 2009). Within the framework, barriers to successful implementation can be identified (Getachew-Smith et al., 2022), and the conditions under which the intervention activities are provided can be examined (Nutbeam et al., 1990). Overall, evaluation is understood as a reflective and systematic process, and the design used being flexible depending on the circumstances and context (Parry-Langdon et al., 2003). The value of process evaluation can be external, such as expanding knowledge and improving standards at intervention sites, or internal, by addressing identified concerns, identifying improvements, and informing the transfer of post-intervention practices (French et al., 2020).

Despite the recognition of process evaluation as an essential component of public health intervention research, particularly in assessing complex interventions (Adab et al., 2018), there remains a lack of the use of frameworks or guidelines for process evaluation within health promotion (Lim et al., 2023; Wierenga et al., 2013), as well as significant variation in how process evaluations are conducted (Lim et al., 2023). Additionally, the quality of process evaluations may be low, highlighting the need for greater consistency and transparency (Lim et al., 2023; Wierenga et al., 2013). To address these issues, it is recommended that suitable frameworks, such as the Medical Research Council Framework (MRC) or the RE-AIM framework (Reach, Effectiveness, Adoption, Implementation, and Maintenance), be employed (Lim et al., 2023; Wierenga et al., 2013). However, a systematic review of process evaluations of health promotion interventions in sports settings showed that most evaluations did not comply with any established process evaluation framework. (Lim et al., 2023).

In this study, a school-based sexual health intervention grounded in social marketing components (Lee et al., 2024) was developed and implemented. Given the complexity of the intervention, which incorporates elements from public health, social marketing, and education, evaluating it for potential improvements is crucial. The process evaluation aimed to determine whether the sexual health intervention was executed as intended, identify any additional effects of the intervention, and theorise how these effects were realised. Furthermore, the evaluation aimed to understand how context affects implementation, while also identifying barriers and facilitators that could enhance future interventions.

Three research questions guided the process evaluation:

1. How was the sexual health intervention implemented?

2. What were the mechanisms of impact in the sexual health intervention according to adolescents and teachers?

3. How did the contextual factors affect the implementation of the sexual health intervention?

A sexual health intervention was conducted using a social marketing approach. Social marketing principles formed the basis of the logic model (Table 1), which was developed prior to the intervention. Logic models are required in process evaluation to describe, identify, and organize critical aspects of an intervention that illustrate how it produces change (Office for Health Improvement and Disparities, 2018). As the social marketing evaluation protocol outlined, the logic model's key constructs included inputs, outputs, outcomes, impacts, and return on investment (Lee et al., 2024; Weinreich, 2010, 2025). These elements were considered where applicable; moreover, the model was supplemented with a description of context, which is hypothesised to play an essential role in the success of the intervention.

The social marketing evaluation protocol emphasises advertising awareness and recall, knowledge level, attitudes and perceptions, images of the product, experience with the product, and behaviours (Lee et al., 2024; Weinreich, 2010, 2025). To focus the evaluation more comprehensively on context and the relationships between different aspects of the intervention, the Medical Research Council (MRC) framework was chosen to guide the evaluation process. The MRC framework (Figure 1) for developing and evaluating complex interventions was initially published 25 years ago and updated in 2006 (Moore et al., 2015; Skivington et al., 2021). Its key components are implementation, mechanisms of impact and context. Implementation refers to the structures, processes, and resources through which delivery is achieved and the quality of what is delivered. Mechanisms of impact, on the other hand, involve examining how the intervention produces development and how participants' interactions with intervention activities drive change. Context indicates external factors that may influence the delivery and operation of interventions (Moore et al., 2015).

The Medical Research Council (MRC) Evaluation framework was employed to assess all evaluation aspects and comprehensively understand the intervention.

A purposive sampling technique was employed to select study schools from all lower secondary schools (n = 33) in the specific geographical area of Eastern Finland, classified as rural, peri-urban, and urban (StatFin, 2025). A quasi-experimental design with a control group was utilised, with schools of the same classification assigned to either an intervention or a control group. The study schools were selected based on three inclusion criteria: (1) location in the assigned area, (2) schools' eighth graders in general education classes (excluding special needs classes), and (3) no other sexual health campaigns or projects ongoing or conducted within the past six months before recruitment.

The recruitment procedure commenced by contacting the school principals. Upon receiving their approval, the procedure proceeded by applying for research permits from the municipalities or the school principal, following each school's and municipality's guidelines. Of the six schools invited to participate in the study, 100% responded positively to the recruitment and volunteered to participate (Figure 2). Three schools with 387 eighth graders were selected for the intervention, while three schools with 444 eighth graders formed a control group. Pre-intervention meetings were conducted separately with the health education teachers from each intervention school, either in person at the school or by phone, depending on their preference.

The documents containing research information and consent forms for pupils and their guardians were available in electronic, printed, and video formats. The study's aims, privacy policy, and anonymity were also clarified through the schools' electronic administrative system for communication between home and school, as distributed by the health education teachers. Informed consent was sought from adolescents and their guardians, and ethical approval was obtained from the University of Eastern Finland Committee on Research Ethics (statement 28/2023).

All 13- to 14-year-olds from 19 classes (n = 387, eighth grade) in three intervention schools were invited to participate in the evaluation. Teachers administered the questionnaire at times that suited their schedules, and adolescents who were present and willing to participate completed it, yielding a 65% response rate. Those who chose not to participate in the study did not have to justify their decision. However, it was reported that adolescents or their guardians did not want adolescents to participate, or that health-related burdens affecting schoolwork were cited as reasons for non-participation. Additionally, six of seven health education teachers from these schools participated in the evaluation. Adolescents and teachers were not compensated for their participation in the study.

The development of the sexual health intervention called “Vastuullisex” (transl. “become responsible”) was based on social marketing principles. To the best of our knowledge, this behaviour-change approach (Lee et al., 2024) has not been implemented in Finland to promote adolescents' sexual health, despite being a potentially effective framework for behaviour change interventions (Roger et al., 2023; Stead et al., 2007). Additionally, the Health Belief Model (HBM), which aims to explain the change and maintenance of health-related behaviours (Rosenstock, 1974), guided the intervention development. To identify the evidence base for the intervention's development, a combination of findings from a literature review (Putkonen et al., 2024), The Basic Education Curriculum (Finnish National Agency for Education, 2014), national recommendations (Klemetti and Raussi-Lehto, 2016), and European reports on standards for sexuality education (WHO Regional Office for Europe and BZgA, 2010) along with co-creation with the target audience and other stakeholders, was utilised (Figure 3).

During the co-creation process from January to February 2024 with non-intervention participants, the content and delivery methods of the intervention were operationalised with two health education teachers individually, workshops involving two classes of 13–14-year-olds (n = 32) from one school, and via an online panel discussion with six sexual health education experts from the National Sexuality Education Network. Engaging stakeholders particularly aided in identifying the specific sexual health needs of adolescents in the Finnish context and reminded intervention developers of the importance of inclusivity. The intervention aimed to enhance sexual well-being by influencing adolescents' sexual health-related knowledge, attitudes, and communication skills, and by strengthening their own agency. Additionally, the aim was to raise awareness of sexuality in its broad spectrum. The school-based intervention consisted of three content-specific monthly lessons, allowing participants who missed one session to attend the others. Each lesson lasted 45 min and was conducted by a researcher (H.P), featuring varying themes and different intervention components and delivery methods (Table 2). Since sexuality education often emphasises biological aspects and risk prevention, this intervention deliberately focused its content on broader dimensions of sexuality. The key parts of the intervention were pretested with a non-intervention class of 23 adolescents.

The school-based sexual health intervention aimed at adolescents aged 13–14 was conducted from August to November 2024. In each class, a teacher from the school was invited to observe the session; however, their active participation or teaching was not expected. Nonetheless, teachers were encouraged to provide regular informal feedback throughout the intervention.

The intervention included pre-, post-, and delayed measurements. Process evaluation data were collected using both quantitative and qualitative methods to provide a comprehensive assessment post-measurement. Questionnaires ( Appendix 1) were administered to adolescents (n = 387) over two weeks in November 2024. The variables assessed quantitatively included adolescents' class attendance, their review of the intervention, engagement, and learning. The content areas of engagement (five items) and learning (two items) were measured using a 5-point Likert scale, ranging from 1 (strongly disagree) to 5 (strongly agree), with 3 indicating uncertainty and grouped according to theoretical content (Table 3). Hence, for both content areas, results are presented as the average score of multiple items. Quantitative data were presented using descriptive statistics, while factor analysis and Cronbach's alpha for reliability testing were employed to group the content areas, all conducted with IBM SPSS Statistics version 29.0.2.0.

Qualitative data were collected from November 2024 to January 2025 through interviews ( Appendix 2) with health education teachers (n = 6) who attended intervention visits conducted by the researcher. The semi-structured interviews were carried out in groups (n = 5) or individually (n = 1), and the meetings were hybrid, online, or onsite depending on the teachers' preferences. The interviews were recorded using Microsoft Teams for further transcription. Interview guides were developed based on the established logic model, concentrating on the outputs (intervention content and delivery methods), outcomes (audience response), and contextual factors affecting the implementation of the intervention. Additionally, the learning experiences, benefits, barriers to the intervention, acceptability, and recommendations for future implementation were explored qualitatively. Direct feedback, the researcher's observations, intervention documents, and relevant statistics were also collected. Qualitative data were analysed by applying inductive content analysis (Kyngäs et al., 2019). The AI MS Copilot Enterprise was utilised to improve language and generate ideas.

The adolescents (n = 252) were 13- to 14-year-old eighth graders attending a lower secondary school in Eastern Finland. Approximately half of the respondents (52%) identified as girls, 38% as boys, 5% as belonging to a gender other than the listed options, and 5% preferred not to disclose their gender. Approximately 79% of respondents reported speaking Finnish at home, 13% reported bilingual use of Finnish and another language, and 8% reported using other languages at home.

The health education teachers (n = 6) were all female, aged between 35 and 50. They had an average of nine years of work experience overall and eight years of teaching health education.

The extent to which the intervention engaged its intended target population is defined by the participation rate among the total eligible population, which in this intervention was high, with rates of 73.9%, 86.3%, and 83.2% at the first, second, and third visits, respectively. During the initial visits, absence rates showed minor variations: peri-urban and urban schools had nearly identical rates (26.6 and 26.4%, respectively), while the rural school had a rate of 22.8%. However, teachers from all schools reported significant waves of illness during the first round of intervention. Generally, the rural school had the lowest absence rates compared to peri-urban and urban schools throughout all intervention rounds.

Intervention fidelity, defined as whether the intervention was delivered as intended, was assessed by comparing the planned actions and the actual implementation. The intervention visits took place during the regular school day, either within health education classes (82,1%) or other subjects (17,9%). The intervention was mainly delivered as scheduled: only two of the 57 intervention visits required some reorganization due to unexpected changes involving deputies who were called in to replace absent teachers. The visits were conducted as planned regarding content, although the timetable was slightly adjusted. In one group, all three intervention visits occurred during a class with a lunch break in between. The lunch break minimally disrupted the visits, but the timetable was adjusted accordingly, and the visits were tailored to the situation.

Teachers were invited to join the intervention visits conducted by the researcher. Additionally, teachers informed the researcher about the legal reasons for not leaving pupils unattended, as it is their responsibility to ensure safety (The Basic Education Act, 1998). Principals from each school planned for teachers to participate in the intervention visits. Two of the three intervention schools, comprising 13 classes, had only health education teachers present following each visit. In one school with six courses, the participating teachers were health education teachers or teachers from other subjects. Out of 57 intervention visits, one visit was held without the presence of school personnel. A teacher designated for the visit preferred not to follow it, rationalising the absence by presuming it might be easier for adolescents to open up to the visitor. However, the teacher stated that he was available if needed and came over once during the visit to see if everything was under control.

The content areas and structure of the intervention remained unchanged and were delivered consistently and accurately. However, at the outset of the new theme during the first visits, the researcher familiarised themselves with the amount of time each part required in real-world settings and made some adjustments to the timing within the visit.

The researcher who delivered the intervention has broad experience in supervising and counselling individuals of various ages across diverse sexual health settings. Additionally, the teachers were present to facilitate the lesson if necessary.

Five of six teachers reported continuing to work with the same sexual health themes in their classes, aiming to deepen adolescents' understanding of these topics. Suggestions for best practices in managing sexual emotions and interactions were specifically welcomed, as this theme appeared to be the most challenging and abstract to teach. Three teachers indicated they would incorporate the intervention materials into their teaching. Two teachers were particularly pleased that material regarding sexual rights, presented in “adolescents' language,” from The Family Federation of Finland was introduced, and they stated they would apply it subsequently.

Adolescents reported their satisfaction with the intervention as mainly good or very good, with a mean score of 8 on the Finnish school grade scale, which ranges from 4 to 10. According to teachers' assessments and classroom observations, adolescents approached the intervention with an immediate and openly positive attitude. Only a small number of individuals from different schools expressed their opposition to the visits in a humorously vocal manner.

Nearly 60% of adolescents reported feeling engaged in the intervention, while 4% did not. Notably, approximately 36% were undecided about their level of engagement. By gender, the mean engagement score was 3.6 for girls, 3.6 for boys, 3.3 for other genders, and 3.7 for those who did not want to disclose their gender (where 1 = strongly disagree and 5 = strongly agree with being engaged). When asked about adolescents' learning, roughly one-third indicated that the intervention influenced their views and helped them acquire new information and skills related to sexuality. In contrast, about 17% disagreed with this statement, and approximately half of the respondents remained undecided. However, when the content area of learning was examined further, nearly 45% agreed or strongly agreed with the statement, “I learned something new about sexuality during the campaign”. Across genders, about 49% of girls, 46% of boys, 31% of others, and 50% of those who did not want to disclose their gender reported acquiring new knowledge. In comparison, only about 16% of all adolescents felt that the intervention influenced their opinions on sexuality.

Adolescents appreciated their active involvement and the chance to learn new things during the intervention. Additionally, the themes of open discussion and permission for sexual communication were recognised as essential elements of the intervention.

Adolescents reported that they would have liked to learn more about sexual interaction, dating, expressing sexual emotions, and sexual diversity.

From teachers' perspectives, the intervention component that addressed sexual communication and sexual emotions was linked to success. These themes were identified as the most essential content of the intervention because teachers believed adolescents needed the most support in addressing the above-mentioned abstract topics. Teachers also estimated that it could be challenging for adolescents to find relevant information about these alone. According to teachers, the referred themes suited the intervention well, as they appealed to adolescents the most. Additionally, the topics of sexual rights and consent were regarded as essential by teachers, as they serve as a basis for all sexuality education and well-being.

The content and delivery methods were developed explicitly with 13-14-year-olds and their developmental phase in mind. Nevertheless, the variation in their psychological and physical development was vast, posing challenges for the intervention. An example of this was a slightly humorous video (Link to the website) about consent that was used as a learning resource in the class, where a metaphor of offering tea is employed for consenting to sex. The video sparked a lively discussion, and it became clear that some adolescents did not fully grasp the video's message. In these situations, the essence of the story was simplified and explained in detail using plain language.

According to the teachers, the content of the intervention was well linked to the objectives of sexuality education in the national curriculum. This included an aim to develop pupils' emotional and social skills and their ability to manage various conflicts. Furthermore, the intervention was linked to the curriculum aim of promoting self-awareness, recognising personal values, and identifying and regulating the factors influencing behaviour and learning. The teachers further emphasised that the aim of the national curriculum, which encourages pupils to reflect on issues related to community and equality from a health perspective and to develop responsible solutions in interpersonal interactions, was closely associated with the intervention content.

One teacher also mentioned that the learning goal of understanding the culture of the surrounding communities and the significance of information and communication technology for health was well connected to intervention visit two, which specifically focused on online sexual harassment.

Teachers reported that although some of the intervention topics were covered in curriculum-based sexuality education, the intervention was seen to introduce other, unusual perspectives and something new to these topics. They communicated that receiving a visitor to the class to promote sexual health, even if it partly overlaps with teachers' lessons, was convincing for adolescents and highlighted the importance of the topic. According to teachers and adolescents, the visitor was expected and welcomed by the adolescents into the classroom.

The methods of intervention delivery were reported to be versatile and regarded by teachers as a balanced mix of different learning techniques. There was a shared understanding among teachers that the intervention was inclusive and the content comprehensive enough, offering “everything for everyone.” The delivery methods were deemed suitable for adolescents. The intervention visits differed from regular teacher-led health education classes, and teachers believed that adolescents valued this, as they did not need to take notes or study in a “traditional” way. This sentiment was echoed by adolescents, who appreciated that intervention visits added variety to their school day. Teachers noted that working with example cases regarding sexual rights encouraged most adolescents to participate. Both adolescents and teachers considered a video about consent and the online game-based learning platform, Kahoot!, which focused on dating, feelings, and communication, to be preferred delivery and learning methods.

To improve future delivery methods, teachers characterized group discussions about sexuality as complex for adolescents, noting the challenges in encouraging full participation, even when adolescents could form the groups independently. An individually completed assignment, in which adolescents were asked to list their strengths, proved problematic, particularly under time constraints. A teacher from a rural school noted that diversity-related themes required deeper exploration, as she observed strong attitudes towards them. Teachers suggested that intervention techniques involving adolescents' active participation could have been employed more effectively.

From the teachers' perspective, the timing of the intervention was deemed appropriate, as it laid the groundwork for teaching sexual health later in the same school year. Conversely, some teachers preferred that the intervention occur later, coinciding with when their classes begin to cover sexuality health education.

The visits took place in various physical environments, primarily within classroom settings for teaching academic subjects. They also occurred in art, chemistry, and home economics classes. These environments complicated the intervention process due to their equipment and table arrangements, making it more challenging to maintain adolescents' attention. Additionally, the dynamic nature of the school settings presented minor challenges due to non-functioning IT equipment and unexpected personnel changes.

A restless atmosphere occasionally permeated the classroom. Teachers from all schools recognised that the first intervention round induced the most restlessness, and two attempted to alleviate the unsettled atmosphere by altering the seating arrangement for their classes in the second round. However, the data indicated that this occasional restlessness did not disturb the adolescents and was not reported by them. In contrast, the adolescents described the atmosphere in the classes as enjoyable and relaxing.

“I think it was a smart campaign, and there was a pretty good atmosphere in the class, making it relatively easy to concentrate.”

Teachers reported that group dynamics and peer influence could partly affect the atmosphere in the classroom. Two teachers observed that some pupils, who were usually uncommunicative, became more active during intervention visits. Teachers also reported that the timing of the intervention, whether morning or afternoon classes, and the school setting may have influenced its delivery and the overall atmosphere.

This study aimed to evaluate the implementation, the mechanisms of impact, and the contextual factors of the sexual health intervention targeting adolescents.

The target population was reached effectively, suggesting that embedding the intervention in educational settings was beneficial (Nacke et al., 2021). Furthermore, the results indicate that the intervention visits were completed as planned regarding content, and the required schedule was only slightly modified. Flexibility in scheduling is a core feature of successful intervention delivery (Lim et al., 2023), and although the primary anticipated uncertainties were believed to relate to scheduling or possible timetable changes, these concerns turned out to be minor. Overall, the intervention was delivered consistently and accurately, and its successful implementation was due to close and flexible cooperation with school personnel and committed schools. The positive reception of the sexual health intervention may suggest a need to strengthen teaching in this area or prioritize the topic. Teachers were readily accessible, and collaboration became increasingly informal over time. They were encouraged to contact the researcher with any questions or concerns. The significance of a strong partnership and connection with school personnel cannot be overstated.

Bringing visitors to schools can reinforce the importance of sexual health and diversify daily school routines. A notable strength of this study was the researcher's presence at every visit, which allowed for direct observations and ensured consistency. Additionally, the researcher's background in midwifery and experience working for an NGO in health promotion are considerable advantages. It is essential to notice that although adolescents prefer outside educators to be involved in schools (Corcoran et al., 2020), the presence of their teachers remains critical, especially given the sensitive nature of the intervention. To ensure a well-organized intervention, it is vital to clearly define the responsibilities of teachers, researchers, or other intervention implementers regarding, for example, disciplinary actions taken in the classroom.

The adolescents expressed satisfaction with the intervention and generally demonstrated positive attitudes. Moreover, the safe emotional environment was recognised and appeared to provide learning opportunities. This aligns with previous studies, as adolescents identified the educational climate as crucial in promoting sexual health (Cense et al., 2020; Corcoran et al., 2020). In each class, a standard set of rules for maintaining a safe and trustworthy learning environment was established during the first meeting. This can be seen as an activity that fostered trust between adolescents and the researcher (Lim et al., 2023). During the initial class, it was also discussed how sexuality can evoke various feelings, such as embarrassment or anxiety, and that all these feelings are permitted. Creating a supportive and safe learning atmosphere also stemmed from the teachers' behaviour and presence: they laughed with the pupils, listened attentively, and dedicated time to their classes. The culture of the school and interactions between teachers and pupils in Finland are relatively informal and direct, which benefited the implementation of the intervention. While teachers occasionally found the atmosphere restless, the adolescents did not report experiencing this.

Acquiring new knowledge from the intervention was the least common among adolescents who identified their gender as “other”. Despite considerable efforts to ensure inclusivity and teachers' perceptions that the intervention was inclusive, it remains unclear from adolescents' perspectives whether it adequately addressed all genders. Conversely, adolescents who identified as “other” might have engaged in more extensive reflection on their gender and sexuality prior to the intervention, which may have resulted in higher baseline knowledge and thus less perceived gain from the intervention.

Learning new things and active participation were the most valued elements of the intervention for adolescents. This indicates a desire to be involved rather than bystanders, suggesting significant potential to influence their sexual health and well-being if adolescents are empowered. Evidence shows that sexual health promotion should be addressed with adolescents, not for them (Cense et al., 2020; Coll et al., 2018).

Adolescents also appreciated the chance to talk about sex and sexuality. Open communication can help tackle societal issues such as sexual harassment and consent, which have been a focus of intense public debate recently. Adolescents need support in developing skills to ask for sexual consent (Brady et al., 2022), especially given the confusing and dismissive social discussions they might encounter.

As sexual health promotion must evolve, it is crucial to understand the changing needs of adolescents. Based on the results, adolescents would have liked to learn more about sexual interactions, dating, expressing sexual emotions and sexual diversity. Some of these specific needs have been identified in previous studies (Bauer et al., 2020; Cense et al., 2020; B. Johnson et al., 2016).

Teachers and adolescents assessed that watching a video about consent, discussing it afterwards, and playing Kahoot were the best delivery methods. Adolescents value diverse teaching approaches (Cense et al., 2020; Seiler-Ramadas et al., 2020), and while competitive and cooperative learning can enhance the learning process through excitement, enjoyment, and engagement (Haruna et al., 2018), it is essential to recognise that these methods might not suit everyone.

The MRC evaluation framework and logic model based on social marketing effectively guided the evaluation process. The quality assessment for process evaluation (Grant et al., 2013; Lim et al., 2023) was followed, contributing to the study's reliability. The process evaluation data were analysed before the outcomes were known to prevent biased interpretation (Bartelink et al., 2022).

There are several limitations to consider. First, the data for process evaluation were gathered at a single point in time. Consequently, not all necessary remarks related to the intervention may have been captured. Second, the process evaluation questionnaire, filled with the outcome questionnaire concurrently, might have been too lengthy for the target group, as many adolescents answered “I don't know” to the evaluation questions. Additionally, some intentional false reporting likely occurred. It is recognised that process data collection in real-world settings and the recruitment of participants for process evaluations can be challenging (French et al., 2020). Third, even if the process evaluation data were analysed before the intervention outcomes to prevent biased interpretation, the relationship between the process evaluation and outcome evaluation has not yet been assessed. Therefore, their interconnections cannot be summarised here. Fourth, the continuity of the intervention depends on teachers' activities, which are not monitored by the research team. Furthermore, the short duration of the intervention may have limited its impact on adolescents' sexual views.

Significant ethical concerns arise when researching a sensitive topic within a vulnerable group. Even if the feedback was mostly positive, it is likely that some adolescents may have difficulties with sexuality; they may have experienced sexual harassment or hold conflicted attitudes towards sexuality for various reasons. Adolescents were advised to contact a public health nurse, a parent, or a friend if any concerns arise. However, this could have been emphasised more strongly. Finally, it must be acknowledged that interventions or theme days cannot replace long-term, systematic, age-specific sexuality health education.

According to this study, a school-based sexual health intervention, characterised by its comprehensive approach and diverse delivery methods, was both feasible and acceptable to the target group. However, engaging adolescents in the evaluation process proved somewhat challenging, as their views were only available post-intervention, despite informal chats and discussions during the intervention visits. To obtain a more robust evaluation throughout the process, future research should prioritise establishing a systematic assessment that collects data multiple times. It would also be beneficial to explore how adolescents themselves wish to contribute to the evaluation. Furthermore, scaling up the intervention could be achieved by engaging other key stakeholders, such as youth organisations and parents, while considering cultural considerations and the importance of strong partnerships.

This study enhances the understanding of process evaluation and its significance in sexual health interventions, providing insights from real-world experiences in developing, implementing, and evaluating such interventions. The key to successful implementation was close cooperation of school personnel and a clear yet flexible plan for achieving it. The mechanisms of impact were primarily evident in positive attitudes towards the intervention among adolescents and in the majority's feelings of engagement. Additionally, the topics of the intervention were closely linked to curriculum-based sexual health education, thereby supporting and complementing it. Learning can be regarded as generally satisfactory following the intervention, although adolescents reported that it had relatively little influence on their opinions.

Contextual factors facilitated implementation in familiar settings for adolescents and contributed to a reported sense of a safe psychological environment. The social environment, including group dynamics and peer interactions, may have influenced implementation. Challenges regarding the contextual factors were observed in some physical settings, which were considered impractical. The findings of this study are beneficial in raising awareness of process evaluations and their value in sexual health promotion, as well as in planning and updating school health education for this age group.

The artificial intelligence MS Copilot Enterprise was utilised to improve language and generate ideas.

Background Information

Your age: _________

Gender:

• Girl

• Boy

• Other

• Prefer not to say

School: ___________

Class: ___________

Languages spoken at home:

• Finnish

• Finnish and some other language(s)

• I don't speak Finnish at home

Did you attend the first theme lesson, ‘My body is precious, my mind is precious, I am precious!’?

• Yes

• No

Did you attend the second theme lesson, ‘Give a Little Respect'? Say no to sexual harassment’?

• Yes

• No

Did you attend the third theme lesson, ‘I Like You So Much My Heart Could Burst!’?

• Yes

• No

• What did you consider the best thing about the campaign?

• What topic would you have liked to learn more about?

• What school grade (4–10) would you give the Vastuullisex campaign?

• Is there anything else you would like to say about the Vastuullisex campaign?

Thank you very much for your response!

1. Age of the participants

2. Educational institution where the teacher works

3. Total work experience in years

4. Work experience in teaching health education

1. The linkage to the curriculum-based sexual education

2. The strengths of the intervention content

3. The estimation of how pupils received and comprehended these topics

4. Development areas related to intervention content in the future

1. Evaluation of the methods used in the intervention

2. Strengths related to the implementation of the intervention

3. Development areas related to the implementation of the intervention

4. Evaluation of the inclusiveness of the intervention or lessons

5. Unexpected factors affecting the intervention practices

1. The suitability or feasibility of the intervention

2. Pupils' reception of the intervention assessed by teachers

3. Pupils' commitment to the intervention as assessed by teachers

4. Atmosphere and working peace during the intervention classes

5. Functionality of the physical spaces used for the intervention

6. Group dynamics of the students and its impact on learning

7. Timeliness of the intervention

8. Benefits of the intervention for pupils

9. Added value of the intervention to health education's sexual education teaching