Speaking in numbers: The effect of reading performance on math performance among immigrants

•We estimate the causal effect of reading performance on math performance among immigrants.•We combine PISA data with an innovative measure on language differences.•Simple OLS regressions of reading on math performance are prone to ability bias.•Exploit exogenous variation in reading performance due to differences in age-at-immigration across different linguistic distances.•We find strong effects of reading performance on math performance.

This paper is the first to estimate a causal effect of immigrant students' reading performance on their math performance. To overcome endogeneity issues due to unobserved ability, we apply an IV approach exploiting variation in age-at-arrival and the linguistic distance between origin and destination country languages. Using four PISA waves, we find a strong influence of reading performance on math performance, highlighting the importance of early language support for immigrants for their educational career.