This study investigates how two newcomer students, Elena and Martin, identified with and in science within the context of a classroom utilizing a reform-based science curriculum where instruction occurred only in English. Using ethnographic case study methods, we drew from anthropological theories on identity development and sociocultural perspectives on language development to argue that as English language proficiency mediated the newcomers' access to academic content, the viability of the newcomers' authored science-related identities in practice were contingent on the dynamics generated within their small groups. We conceptualized the small groups as microfigured worlds and show how these spaces, in particular the kinds of patterned activities and practices that emerged in relation to the use of language brokering and/or code switching, mediated the kinds of identities in practices that the newcomers were able to author. We end the article by interpreting our results in relation to how Ms. Hall, the teacher, structured her classroom and discuss the relevance of race/ethnicity and gender. We conclude with suggestions about how focusing on group, or peer networks, might inform both theory and practice around how newcomers, and emergent bilinguals more broadly, engage in science.