Around half of children in low-income countries have elevated blood lead levels. What role does lead play in explaining low educational outcomes in these settings? We conduct a new systematic review and meta-analysis of observational studies on the relationship between lead exposure and learning outcomes. Adjusting for observable confounds and publication bias yields a benchmark estimate of a 0.12 standard deviation reduction in learning per natural log unit of blood lead. As all estimates are non-experimental, we present evidence on the likely magnitude of unobserved confounding, and summarize results from a smaller set of natural experiments. Our benchmark estimate accounts for over a fifth of the gap in learning outcomes between rich and poor countries, and implies moderate learning gains from targeted interventions for highly exposed groups (≈ 0.1 standard deviations) and modest learning gains (< 0.05 standard deviations) from broader public health campaigns.