Teachers' training, class size and students' outcomes: Learning from administrative forecasting mistakes.

This article uses a feature of the French system in which some novice teachers start their jobs before receiving any training. Moreover, thanks to administrative mistakes in forecasting the number of teachers, trained and untrained novice teachers are similar in 1991. We show that they are assigned to similar classes. In addition, we show that the same sample can be used to estimate the causal effect of class size. Our findings are: (1) teachers’ training substantially improves students’ test scores in mathematics, except for initially low‐achieving students; (2) a small class is beneficial to students, especially to low‐achieving ones.