This policy brief summarises new research findings from two studies using Young Lives data to determine what works for improving the quality of education in public secondary schools in Peru. It focuses on factors that contribute to improved performance in relatively difficult and disadvantaged circumstances, to identify successful approaches to improving school effectiveness. Our research uses a comprehensive mixed-methods approach to understanding the factors underpinning improved school effectiveness – the first study of its kind in Peru. We also evaluate the impact of Peru’s Jornada Escolar Completa (JEC) reform on improving educational outcomes across a selection of public secondary schools, through a package of measures to both increase the quantity of schooling hours and the quality of schools and teaching. The brief presents key policy recommendations in response to these findings.