The main objective of this research was to investigate the pedagogical activities in Science classes that are related to the development of reading and writing skills. Taking into account that the acquisition of written language is a commitment of school education commitment, especially in current graphocentric societies, the present study sought to reflect on possible contributions of Science classes to the development of readers and writers. Three sixth grade classrooms located in Rio de Janeiro were observed along with their science teachers. Semi-structured interviews were conducted both with the teachers and students, and the didactic materials used by them were analyzed. The theoretical-methodological framework is based on Bakhtin and on the social interactionist perspective of language. Goodson s sociohistorical theory was used for understanding the characteristics of Science as a school discipline. Results show that Science class space-time is also space-time for reading and writing. Science knowledge is constructed in school through written language and, because of that, many different activities involving reading and writing take place in Science classes. The teachers mediate the interaction between the students and the written language, guiding their reading and textual production processes. Through mediation, they act in the mobilization of strategies and systems of knowledge (linguistic, world and interactional ones) that contribute to students’ reading and writing skills, making the meaningful construction of texts possible. When talking about the texts, primary and secondary discourse genres appear, as the teachers bring everyday elements to the interaction between text and students and, at the same time, contribute to the complexity of language, bringing it closer to the written form. In the discursive chain of the classroom, texts of various genres are used and are associated with the different curricular traditions of Science as a school discipline. The teachers mix in their speech different conceptions of reading and writing: from one that focuses on the structure of the text to another that sees it as a social interaction among author-text-reader. The wide presence of written discourse and activities that deal with text interaction in Science classes show the potential of this school discipline for the development of reading and writing skills. Poor teacher education and infrastructure problems, such as influence of external evaluations and lack of resources, present obstacles to this type of work. It is expected that this research may contribute with reflections about the understanding of Science classes as a space-time for written language that is important for the education of critical and mature readers and authors, and who can then be inserted in a world permeated by social practices of reading and writing.