This article investigates the relationship between reading and writing. We assume that these skills share a number of subskills as can be inferred from models of reading and writing. A set of these subskills are studied for the extent to which they can explain the common variance (correlation) between reading and writing. Data from a sample of Dutch students performing reading and writing tasks in Dutch and English as a foreign language, as well as tests for various Dutch and English subskills, both declarative knowledge and processing fluency, were analyzed using structural equation modeling to estimate residual correlations between reading and writing, controlling for subskills. Results show that declarative linguistic knowledge is a more likely source for the common variance between reading and writing than processing fluency, and the subskills seem to play a larger role in EFL reading and writing than in L1 reading and writing. However, the EFL patterns seem to develop in the direction of the L1 results in the course of three grades.