This study investigated the differences in physical activity (PA) at recess and school-related social factors, and described school PA promotion processes and staff experiences at four lower secondary schools from the Finnish Schools on the Move programme. Recess PA, peer relationships at school, relatedness to school, and school climate were assessed via surveys with eighth-grade students in spring 2011 (n = 385) and spring 2013 (n = 373). Local contact people in the school projects (n = 6), school staff (n = 83) and principals (n = 3) provided information on the PA promotion process via telephone interviews and surveys. Differences in student-level data in years 2011 and 2013 were analysed by gender using two-way ANOVA. Data on school processes were analysed using a combination of classification, narrative approach and content analysis. In two of the four schools, male students reported higher levels of recess PA in 2013 compared to 2011. In three schools, school-related social factors did not differ between 2011 and 2013. School cultures and routes towards a more physically active school day differed; the project was highly visible in all schools, but staff participation varied. More research is needed to determine the effective physically active strategies to promote positive social well-being and to enhance staff engagement.