This article presents cases of three young people who represent the "New Mainstream" of the 21st-century classroom as they engaged in a year-long research and writing project. Focal students were classmates who represented the linguistic and cultural diversity of today's New Mainstream: a transnational Mexican-origin bilingual female, an immigrant Mexican-origin bilingual female, and a Caucasian English-speaking male. Cases focus on the young people's language and literacy histories and key patterns related to their language use in school as examples of the complexity of students who represent the New Mainstream. Findings suggest the need for a reframing of the notion of "mainstream" and expanded definitions of academic language to better address the realities of New Mainstream classrooms. (Contains 2 notes and 1 table.)