When Better Teachers Aren't Enough: An Experimental Evaluation of Teacher Training Programs in El Salvador

Despite billions spent annually on teacher training, rigorous evidence on standalone in-service programs remains scarce, as most evaluated programs bundle training with curriculum or material reforms. We address this gap through a large-scale randomized controlled trial with 338 schools and over 6,000 students in El Salvador. Teachers are randomly assigned to either a control group or one of three training programs focusing on (i) content knowledge, (ii) pedagogical knowledge, or (iii) a combination of both inputs. We find lasting effects on teacher content and pedagogical knowledge of up to 0.3σ and 0.5σ respectively one year after program end. Yet, this only changes teachers' classroom practices in the short-run and does not translate into significant student learnings. The data most closely aligns with a setting where teachers face a dual challenge: introducing new ideas in a rigid environment while navigating the significant learning gaps present among students in later grades.