**Background:** Many European adolescents fail to meet physical activity and nutritional recommendations—only 19% meet WHO physical activity guidelines. Adolescents from lower socioeconomic groups are even less likely to meet these recommendations. Adolescence is a critical period for establishing health behavior patterns, and the WHO recommends engaging young people in intervention design. Citizen Science offers a participatory approach that may also increase interest in science, technology, engineering, and mathematics (STEM), where adolescents from low-income families and girls are underrepresented. The SEEDS project aims to address both challenges: promoting healthy lifestyles and increasing STEM interest among adolescents from deprived areas.
**Methods:** SEEDS is a multi-country cluster randomized controlled trial (c-RCT) in four European countries: Greece, the Netherlands, Spain, and the UK. Each country will recruit 6–8 high schools from neighborhoods within the lowest tertile of socioeconomic status indicators. The target population is adolescents aged 13–15 years. Schools are randomized 1:1 to intervention or control using computer-generated randomization (Research Randomizer software). Allocation is not blinded due to the nature of the intervention. The study aims to recruit 720 adolescents total (90 per arm per country). In each country, 15 adolescents from intervention schools are selected by teachers as 'ambassadors' based on leadership skills, English level, and willingness to participate.
THE PROJECT PROCEEDS THROUGH FOUR PHASES
(1) Recruitment of ambassadors and stakeholders from the Quadruple Helix (government, community, business, academia). (2) Focus groups with ambassadors and stakeholders using the Theory of Planned Behaviour to identify barriers and facilitators of physical activity and snacking behavior, and how science/technology could help. Ambassador training covers the SEEDS project, research principles, and Makeathon preparation. (3) Assessment: all adolescents complete questionnaires at baseline (November 2021) and follow-up (June 2022) measuring primary outcomes (physical activity via HBSC and PAQ-C questions, snacking via HBSC, STEM interest via STEM interest survey, Science Capital via Science Capital survey, STEM career interest via Attitude towards STEM questionnaire) and secondary outcomes (additional country-specific behaviors, determinants per Theory of Planned Behaviour). Sociodemographic data includes gender, age, grade, country of birth, parental country of birth, and Family Affluence Scale. (4) Intervention: Makeathon events (2–5 hours each) where ambassadors, interested adolescents, and stakeholders co-create interventions. Each country implements a 6-month intervention in all intervention schools, which may be peer-led or delivered by researchers/stakeholders, targeting individual behaviors, environments, or structural elements.
**Sample size:** Power analysis using UCSF calculator, with 12 clusters per group, type I error 0.05, 80% power, effect size 0.35, ICC 0.06, requires 720 subjects (360 per group). Based on HBSC data (mean 4.17, SD 2.07 days/week physical activity).
**Statistical analysis:** Continuous normal data as mean±SD, non-normal as median (IQR), categorical as n(%). Baseline comparisons using t-test, Mann-Whitney, or χ². Multiple imputation for missing data. Effectiveness evaluated using multilevel mixed models controlling for sociodemographics and school-level clustering. Subgroup analyses by country and sociodemographic variables. Two-sided p<0.05 considered significant.
**Key Results:** This is a protocol paper; no results are reported.
**Clinical Implications:** The SEEDS project aims to provide new insights into how adolescents and stakeholders perceive barriers and facilitators to healthy active living, how Makeathon events can support adolescent-led intervention creation, and whether SEEDS activities change behavioral and STEM outcomes in adolescents from deprived areas. By focusing on lower socioeconomic groups across four European countries, the project has potential to contribute to reducing socioeconomic inequalities in health and STEM career participation. Limitations include context-specific interventions differing between countries (mitigated by standardized core questions and protocols), reliance on self-reported questionnaires (mitigated by validated instruments from HBSC), and a follow-up period of 6–8 months that may not capture sustained effects. The COVID-19 pandemic poses additional risks addressed through flexible protocols allowing online delivery.