We examined the direction of the relation between morphological awareness and reading/spelling skills in 2 languages varying in orthographic consistency (English and Greek) and whether word reading fluency and vocabulary mediate the relation between morphological awareness and reading comprehension. One-hundred and 59 English-speaking Canadian and 224 Greek children were assessed 4 times between Grades 1 and 3 on measures of morphological awareness, phonological awareness, word reading fluency, and spelling to dictation. Vocabulary was assessed at the end of Grade 2 and reading comprehension at the end of Grade 2 and at the beginning of Grade 3. Cross-lagged analyses showed that earlier morphological awareness predicted later reading comprehension and spelling in both languages and reading fluency in English. The effect of morphological awareness on reading comprehension was not mediated by word reading fluency in either language, but an indirect effect through vocabulary emerged in English. Earlier reading fluency and spelling predicted later morphological awareness before Grade 3 only in English, but morphological awareness began to predict spelling as early as Grade 1 in Greek. Multigroup analyses further showed that the effects of morphological awareness on reading fluency and the effects of spelling on morphological awareness were stronger in English than in Greek. Theoretical implications of these findings are discussed.