This thesis examines how the PAX Good Behavior Game (PAX GBG) functions in mainstream classrooms that include students with diverse special educational needs (SEN). Although designed as a universal preventive intervention, PAX GBG is implemented in contexts characterized by heterogeneous learner needs. The thesis focuses on how the intervention is enacted, adapted, and experienced in everyday classroom practice.

The thesis combines a scoping review with qualitative studies conducted in Swedish primary schools (grades F–3). Study 1 mapped research on the GBG and PAX GBG in relation to students with SEN. Studies 2 and 3 examined teachers’ and students’ perspectives on the use of PAX GBG. Across studies, the analysis focused on mechanisms, participation, adaptation, and variability in how the intervention functioned in practice.

The findings suggest that core components of PAX GBG, such as structured routines, explicit expectations, and positive reinforcement, were recognizable in classroom practice and were often described as supporting predictability, behavioral regulation, and participation for many students, including students with SEN. At the same time, the functioning of PAX GBG varied across students and classroom contexts. Teachers frequently adapted PAX kernels to support participation, and such adaptations appeared important for sustaining the intervention. For some students, PAX GBG also appeared to provide a shared framework on which additional support could build.

However, a smaller group of students with more complex needs participated less consistently or experienced the routines as demanding. In these cases, the intended mechanisms did not fully take hold, and teachers described difficulties in adapting the intervention within the constraints of the classroom.

Taken together, the findings suggest that PAX GBG can function as a meaningful component of inclusive classroom practice in mainstream education, but that its accessibility for students with SEN is shaped by how it is adapted and supported within broader educational support systems. The thesis contributes a more context-sensitive understanding of how universal interventions operate in heterogeneous classrooms and highlights the importance of aligning classroom practices with structured systems of support.