<p>Morphological awareness is the metalinguistic ability to reflect on morphemes. The present study investigated the effects of a morphological awareness intervention program on spelling and reading performance in two 4th grade classes (one control group and the other experimental) of a public school in Rio de Janeiro. Participants were 47 children who were tested for morphological, phonological, and syntactic awareness; vocabulary; non-verbal intelligence; reading; and writing. Initially, control and experimental groups did not differ significantly in the measures investigated. After the intervention, the experimental group showed significant improvements in spelling morphologically complex words and words with contextual rules of Portuguese language, such “as always spelling “m” before the letters “p” and “b.” There were no significant results for reading. The results suggest that in an orthography such as Portuguese, with spelling ambiguities, the intervention benefits children to advance in writing. In reading, graphic cues are already present; it is possible that phoneme to grapheme correspondence rules are sufficient for reading accuracy.</p>