performing over 85%. This is a striking degree of classroom level heterogeneity given the fact that within a given school all teachers serve a roughly homogenous student population, deliver the same curriculum, and work under the same set of management and institutional conditions. Gaps of this magnitude in the instructional time different students experience could be expected to affect learning outcomes at the classroom level.

One positive implication of the Latin America research is the scope for school-level performance gains through greater diffusion of the best teaching practices within schools. Indeed, the exchange of practice among teachers in a school is a core strategy in high-performing East Asian systems, such as Japan’s lesson study (Easton, 2008; Yoshida, 1999; Doig and Groves, 2011), Singapore (OECD, 2013) and Shanghai (Liang, 2015). Sustained school-level learning improvements are also reported in Ontario, Canada through a program which provided schools with feedback on their teachers’ classroom-level learning outcomes and external coaches who encouraged school personnel to work together to share practice and improve instruction (OECD, 2011; Mourshed et al. 2011; Fullan, 2013). Fullan calls this the creation of a "professional learning community" within the school.

A hypothesized theory of action is that promoting and supporting school-level professional interaction among teachers may improve results through four channels. First, by increasing the amount of transparency about differential teacher performance within a school it can create “lateral accountability” or peer pressures on teachers to exert more effort towards improving their performance. Second, it can provide teachers with “curated” pedagogical or classroom management techniques (used effectively by their peers) that are clearly relevant to their school context. Third, it can transfer knowledge through modeled practice, which may be inherently more effective in supporting the adoption of new practices and behaviors than off-site, lecturebased training. Fourth, it can guarantee continuous support and reinforcement for the new behaviors from the school director and peers if the “whole school” is engaged in and committed to achieving improved classroom practice. However, countervailing factors include possible unwillingness among teachers to acknowledge differences in classroom effectiveness and weak extrinsic (salary, promotion, managerial oversight) incentives to reward improvements. A final issue may be that even if teachers were able to improve their classroom practice by, for example, devoting more time to instruction, weaknesses in teachers’ content mastery could limit the impacts on student learning.

This paper presents the results of a randomized evaluation of the Ceará program. We show that the program increased teachers’ use of class time for instruction, by reducing the time spent on classroom management and time off-task. The program also increased teachers’ use of questions during their lessons, consistent with the coaching program’s goal of encouraging more interactive teaching practice. The treatment schools also registered an increase in student engagement. Finally, consistent with the program’s strategy of promoting greater interaction among teachers, the improvements in schools’ average results were achieved by reducing the within-school variation in teacher practice. There is encouraging evidence that in most dimensions, schools and classrooms with the weakest performance improved the most.

Over the 2015 school year, these changes in teacher practice raised student learning in math and Portuguese on both the Ceará state assessment, SPAECE, and the national secondary school exit exam, ENEM. Learning gains were statistically significant, as we can control for individual students’ prior-year learning outcomes. Performance in the treatment schools was 0.05 SD higher in Portuguese and 0.08 SD higher in math on the SPAECE test and 0.055 SD higher in Portuguese and 0.04 higher in math on the ENEM test. For classrooms with the highest average time on classroom management, rather than instruction, at baseline, the learning gains were significantly higher: 0.12-0.17 higher on SPAECE and 0.14-0.15 SD higher on the ENEM test. Finally, implementation fidelity had a large impact on learning results. In schools whose pedagogical coordinator scored “excellent” on a final certification test, SPAECE scores were 0.13-0.23 SD higher and ENEM scores were 0.13-0.17 SD higher. These results suggest that the combination of teacher feedback and expert coaching is a promising strategy for raising school quality.

Section 2 describes the context, the intervention, and the research questions. Section 3 describes the instruments used and the sample. Section 4 presents the impacts on teacher practice and classroom dynamics and analyzes threats to the experiment. Section 5 analyzes the program’s impacts on student learning. Section 6 presents a cost-effectiveness analysis. Section 7 summarizes our conclusions and their implications for education policy in Brazil and other settings.

# **2. Intervention and Experiment Design**

The Northeast state of Ceará, with 8.9 million people, is the 8th most populous in Brazil. With a GDP per capita estimated at $2,500, it is also one of Brazil’s poorest states. While municipalities manage the provision of pre-school and primary education (grades 1-9) in Brazil, states are responsible for the threeyear cycle of secondary education. Ceará state’s education secretariat manages 621 schools with a total of 3