PURPOSE: to analyze the relevant variables in the acquisition of morphological (e.g. cadeiras) and lexical (e.g. lápis) codas, with the fricative /S/ at the end of the word. METHODS: we examined data from 15 children, 10 girls and 5 boys, aged between 1:7 and 3:7, monolingual speakers of Brazilian Portuguese, whose speech was recorded each fifteen days during one year. The speech data were obtained through recreating activities, transcriptions and review. Next, the data were analyzed based on the Statistical Program VARBRUL. RESULTS: the program selected speech part and gender as relevant to the correct production, for both variable codas. Among speech parts, pronouns and adverbs were considered important to achieve correct production in both coda types. In addition, the program selected: the nouns, to the lexical coda, and the numerals, to each morphological coda. Tonicity and precedent context variables were fundamental to the production of lexical codas, with a higher probability for correct production when there is a tonic syllable and the precedent context shows a dorsal vowel. Age was also deemed to be an important variable to the production of morphological coda, with a statistically significant result from older children. CONCLUSION: it was observed that speech parts and gender were important for the acquisition of both coda types, however, the process of /S/ production in both cases showed distinct variables, and it could be related to the fact that the child had singular characteristics in their own acquisition process.