The current study examined the contexts in which a preschool teacher professional development intervention was more versus less effective in improving student outcomes. We used a fixed intercept, random coefficient (FIRC) modeling approach to explore the contextual characteristics inside and outside school walls that predicted differential effectiveness of the NCRECE teacher professional development experimental intervention on students' language and literacy skills, executive functioning, and learning behaviors (N = 1,230 children and 317 teachers within 192 center-based preschools; the majority of preschools were publicly funded). Overall, most characteristics inside and outside school walls were not associated with treatment impact on student outcomes. The only exception is that some characteristics outside school walls were associated with treatment impact on students' executive functioning skills, where the professional development intervention (course and/or coaching) had a more positive effect on children's executive functioning in preschools located in neighborhoods with lower levels of institutional resources and lower structural/social processes. Findings are discussed in terms of implications for large-scale teacher professional development programs and systems.