Several studies concerning reading comprehension have been published aiming to offer better learning opportunities in this context. Differently from other studies, this study aims to investigate how the concept maps, which have already been used in other contexts, are related with the teaching of Portuguese as L1. This study is based on ethnography principles and analyses the summaries of students in two phases, one before the intervention and the other after the intervention with concept maps. Besides, it triangulates the data from the summaries with information of interviews with ten students, which aim at elucidating how the texts were summarized. We also used field notes, the ranking of the summaries in inverted order by the teachers of Portuguese and Text Production, and information about the performance of a class of first year High School of a State School in Petrópolis, Rio de Janeiro. The results of the first summaries indicate that the majority of the students copy parts of the original text trying to summarize them. Other students copy and paste parts of the text using discourse markers which force cohesion, creating meaningless sentences. On the other hand, the summaries from the second phase were shorter, which indicates better capacity of summarizing. Consequently, the volume of copy also decreased, indicating that, at least in some cases, an increase of comprehension seems to have taken place. These results suggest that a more systematic intervention with concept maps can indicate ways to promote development in the reading and in the comprehension process of texts of varied sources.