The aim of the study was to investigate prospective relationships between reading and writing performance during the first grade of primary school. The data was collected from 83 Finnish-speaking children who were examined four times on reading, spelling, and productive writing skills during the first grade. At the beginning of the school year, they were also tested on initial reading skill. The results showed that reading and spelling manifested a reciprocal relationship during the first semester: reading performance increased subsequent spelling proficiency, and spelling skills enhanced subsequent reading. Later on, however, reading predicted spelling in a less reciprocal association. In turn, productivity of writing predicted subsequent reading performance during the first grade although the reverse was not true. The results suggest that it may be important to emphasize the support which compositional writing may offer to the development of reading.