Relations between reading and writing have been studied extensively, but the less is known about the developmental nature of their interrelations. This study applied latent change score modeling to investigate longitudinal relations between reading and writing skills at the word, sentence, and text levels. Latent change score models were used to compare unidirectional pathways (reading-to-writing and writing-to-reading) and bidirectional pathways in a test of nested models. Participants included 316 boys and girls who were assessed annually in Grades 1 through 4. Measures of reading included pseudoword decoding, sentence reading efficiency, oral reading fluency and passage comprehension. Measures of writing included spelling, a sentence-combining task, and writing prompts. Findings suggest that a reading-to-writing model better described the data for the word and text levels of language, but a bidirectional model best fit the data at the sentence level.