Based on evidence derived from studies conducted mostly in the United States, many low- and middle-income countries are investing in early childhood education (ECE), with high expectations that it will improve academic outcomes, increase human capital, promote economic growth and reduce economic inequality. In Chile, there has been a great expansion of ECE provision. Still, children's language skills are below average, and there is a significant gap between socioeconomic groups. "Un Buen Comienzo" ("A Good Start", UBC) was a cluster-randomized experiment of a two-year professional development program conducted in Chile that aimed to improve the quality of public preschool education and the outcomes of participating children. UBC provided 12 monthly workshops and 24 biweekly in-classroom teacher coaching sessions to promote adoption of strategies to improve children's language and literacy, with supporting interventions for children's health, socio-emotional development and family involvement. Findings suggest that Continuous Quality Improvement Learning Collaborative (CQI) works in part through changing the role of teachers in the school, supporting their own leadership and collaboration, and moving away from a culture of strict accountability (i.e. judgment) to one of facilitated and shared growth. Tables are appended.