This paper examines the impact of COVID-19 school closures on student learning outcomes using data from the Programme for International Student Assessment (PISA). The study finds that school closures led to significant learning losses, with math scores declining by an average of 12 points, or 14% of a standard deviation, equivalent to about seven months of learning. These losses were more pronounced for students in schools with longer closures, boys, immigrants, and disadvantaged students. The duration of closures was a key factor, with countries experiencing longer closures seeing greater learning losses. The paper also highlights the economic implications, estimating that the average learning loss translates to a GDP growth loss of approximately $17 trillion globally. The findings underscore the need for effective learning recovery strategies to mitigate these losses.This paper examines the impact of COVID-19 school closures on student learning outcomes using data from the Programme for International Student Assessment (PISA). The study finds that school closures led to significant learning losses, with math scores declining by an average of 12 points, or 14% of a standard deviation, equivalent to about seven months of learning. These losses were more pronounced for students in schools with longer closures, boys, immigrants, and disadvantaged students. The duration of closures was a key factor, with countries experiencing longer closures seeing greater learning losses. The paper also highlights the economic implications, estimating that the average learning loss translates to a GDP growth loss of approximately $17 trillion globally. The findings underscore the need for effective learning recovery strategies to mitigate these losses.