Adolescents worldwide have recently experienced a concerning decline in life satisfaction. Multicomponent positive psychology interventions (MPPIs) have shown effectiveness in improving adolescents’ psychological well-being. This chapter explores factors that may have contributed to adolescents experiencing varying benefits from the school-based MPPI Study with Strength, the aim of which is to enhance student well-being. The exploration focused on whether participant characteristics or levels of engagement in the intervention moderated its effects. The intervention, combining positive psychology and cognitive therapy, was developed collaboratively with participating upper secondary schools. The final sample included 342 students from ten schools. Self-report measures assessed immediate and long-term intervention effects on student well- and ill-being. Findings showed no significant moderation effects of homework completion, mindfulness meditation, attendance, or teaching mode (in-person or remote) on well-being or ill-being post-intervention or at follow-up. Similarly, baseline ill-being did not moderate post-intervention or follow-up well-being. However, homework completion predicted students’ perceived changes in well-being and in the intervention’s usefulness. Unexpectedly, more frequent meditation was linked to less perceived benefit from the intervention. The findings highlight that motivation may play a crucial role in MPPIs and suggest flexibility in their administration, offering valuable insights for future application of positive psychology with adolescents.