This article explores the experiences of teaching assistants from nonmainstream backgrounds in a predominantly white institution (PWI) of U.S. education. We focus on how such teaching assistants experience and respond to "microaggressions" or subtle challenges to their teaching based on race and ethnicity. We also explore the consequences of microaggressions for teaching assistants' future career plans. Analyses of life history interviews show how processes of microaggressions permeated teaching assistants' relationships with white prospective and cooperating teachers. The authors suggest ways to interrupt these in teacher education programs.