This article reports on the construction process of inclusion/exclusion for high school chemistry students in two schools in Belo Horizonte, the capital of Minas Gerais State, Brazil. We examined the interactional accomplishment of inclusion/exclusion of four students, two from a private school and two from a public school. The aim of this article is to describe these students' stories of inclusion/exclusion and to discuss what motivated them to learn chemistry in the classrooms investigated. To learn chemistry, students need to develop an individual understanding of the social language of the discipline. Inclusion/exclusion is accomplished interactively as members of different communities make choices about how to participate, involve others, and direct their actions. Such interactions are mediated by the teacher, and thus, through discourse, the collective group establishes certain learning opportunities. (Contains 1 note.)