This study reports the effects of a distributed professional development model emphasizing reading comprehension and vocabulary practices in social studies on the content knowledge, vocabulary, and reading comprehension outcomes of upper elementary students identified as English learners (ELs). Schools were randomly assigned to one of three conditions: researcher-supported professional development (PD), school-supported PD, or business as usual (BAU; typical instruction). Findings from a prior randomized control trial revealed significant effects for both treatment conditions when compared with the BAU group for content knowledge, vocabulary learning and reading comprehension in content (Capin et al., 2020). This analysis addressed three related follow-up questions: (1) Does treatment affect ELs and non-ELs differently?; (2) Does treatment affect students differently depending on the school-wide percentage of ELs?; and (3) Does treatment affect EL students differently from non ELs depending on the school-wide percentage of ELs? Findings revealed that ELs in treatment conditions outperformed ELs in the BAU condition and school level percentage of ELs had an impact on EL vocabulary performance.