This paper contributes to the growing body of evidence on the effects of school closures on learning outcomes, focusing on a recent event in a developing country. During the 2009 H1N1 pandemic outbreak, a significant number of public schools in São Paulo state, Brazil, extended the winter break by two to three weeks. By employing double- and triple-difference estimates, the study reveals that even such a relatively short period of school closure can result in a learning deficit equivalent to six to nine weeks of regular schooling. Furthermore, the findings indicate that the adverse impacts were more pronounced among students performing below the expected proficiency level in math, suggesting disproportionate effects on schools with a higher percentage of academically challenged students. Moreover, the research underscores the role of school decentralization, revealing that municipal schools exhibited greater resilience in mitigating the negative shock compared to state-run schools. This observation aligns with the broader evidence highlighting the advantages of decentralized governance structures in responding to crises within the education sector.