Doctoral student Leonardo Rosa will present the results for a Lemann Center paper on the “tempo integral” high school reform in Pernambuco. The paper has been able to identify the effect of full day high schools on student mathematics performance in Pernambuco using a difference in difference in differences approach, thanks to the staggered implementation of the reform over the past seven years. Leo will discuss the methodology and the results, with particular emphasis on whether the rather large impact of the reform is due to a large increases in the time mathmatics is taught or other aspects of the reform.