We know a great deal about children’s first steps into reading. Here, we explore how they become more sophisticated readers, learning to read complex words. Theoretical accounts predict that one key factor is morphological awareness, or awareness of the minimal units of meaning in language. And yet empirical studies have yet to clarify whether morphological awareness has a stronger relation to the development of reading skill for words with multiple morphemes in particular (i.e., morphological decoding) or to the reading of a whole range of words. We examined this question in this study by contrasting the role of morphological awareness in the development of morphological decoding and of broader word reading skill. Participants were 197 English-speaking children who were followed from Grade 3 to 4. We conducted longitudinal analyses that included stringent autoregressive controls to capture the determinants of gains over time, as well as controls for vocabulary and phonological awareness. Structural equation modeling (SEM) path analysis with this set of controls revealed that morphological awareness predicted significant unique gains in morphological decoding from Grade 3 to 4 with no such unique contributions to broader word reading skill. These findings clarify the role of morphological awareness in supporting children in developing the ability to read morphologically complex words, supporting a more targeted role for morphology in theories of word reading development.