Description: This contribution develops a discursive analysis of classroom interaction as speech genres. On the one and, the main purpose of the research is to bring about a discursive analysis - based on Bakhtinian Speech Genres Theory - of classroom interactions as different school speech genres. On the other hand, to show how multiple secondary genres that circulate out of school, are transposed to classrooms as objects to be taught and tools to teaching. Methodology: Data consists on videotape transcription of public school classes on Sciences, Mathematics, Portuguese Language, History and Geography, from 1st to 8th grades, composing a corpus of 57 classes' transcripts on different matters and grades. Data was collected in a large public school in the city of São Paulo, Brazil. A methodological discussion focused on the question of how to isolate, through the multimodal actions of the teacher, the essential dimensions of a discursive object being taught is developed. Conclusions: Results show that taking utterances as a unit of analysis and following a Bakhtinian sociological method when analyzing classroom data lets us capture essential dimensions of language as an object being taught and as a tool to teaching.