Opening the black box: Intervention fidelity in a randomized trial of a preschool teacher professional development program.

Un Buen Comienzo [A Good Start] was a professional development program implemented with prekindergarten and kindergarten teachers in Chilean public schools serving low-income families. In a randomized trial, the program showed moderate to large impacts on classroom quality but no impacts on targeted child outcomes. To unpack these findings, we examined intervention fidelity (IF) in both treatment and control groups. Specifically, the study...