ABSTRACT In this article, we investigate the presence and the absence of commas in a longitudinal sample of texts of the genre report written by 11 to 15 years-old students from a school in the countryside of São Paulo State. Our hypothesis is that the comma is used when syntactic boundaries match the prosodic ones. The prosodic constituents are formed from syntactic and phonological information, according to principles defined in the Prosodic Phonology theoretical approach. The characterization of the conventional commas and the non-conventional absences of commas was made from the identification of syntactic boundaries in which they should or could be placed, taking as reference a Brazilian Portuguese grammar. The results were that the conventional comma increases during the years of schooling, as expected. However, the presence and absence of comma rates changed depending on the type of syntactic structure and on the occurrence of intonational phrase boundaries. Comma occurred predominantly in positions where intonation phrase boundaries match major syntactic boundaries, as a sentence boundary. In turn, the comma systematically does not occur in positions where the syntactic and prosodic boundaries do not match.