We use aggregate PISA data for 19 countries over the period 2000–2009 to study whether a higher share of immigrant pupils affects the school performance of natives. We find evidence of a negative and statistically significant relationship. The size of the estimated effect is small: doubling the share of immigrant pupils in secondary schools from its current sample average of 4.2–8.4 percent would reduce the test score of natives by 1–3.4 percent, depending on the selected group of natives. There is also evidence that – conditional on the average share of immigrant pupils – reducing the dispersion of this share between schools has small positive effects on the test scores of natives. Whether these findings can be generalized to a larger sample of countries is an open question that we leave to future research.