Professional Development at Scale: The Causal Effect of Obtaining an SEI Endorsement Under Massachusetts’s RETELL Initiative

We apply a difference-in-difference design to measure the causal effect of a teacher obtaining an endorsement in Sheltered English Immersion under Massachusetts’s Rethinking Equity in the Teaching of English Language Learners initiative on student’s learning outcomes. More than 35,000 in-service public school teachers completed the semester-long course. We find no effect on English learners’ (ELs) average test scores, but modest positive spillovers for students with disabilities and other non-EL students. Training benefited teachers recently hired by their district but had no effect on longer serving teachers.