With the growing number of students from culturally and linguistically diverse backgrounds in K-12 classrooms across the United States (U.S.), addressing the linguistic and academic needs of English language learners (ELLs) has become increasingly urgent. Nonetheless, many teachers feel under-prepared to meet these needs or believe that supporting ELLs is the responsibility of other specialists. This study addresses the need to prepare mainstream teachers for diverse classrooms by examining the construction of teacher professional identities (TPIs) of mainstream teacher candidates (MTCs). Through multiple case studies of three MTCs, the study reveals (a) the interaction of multiple identity facets, (b) the impact of teacher education experiences on shaping TPIs, and (c) the influence of broader societal diversity issues on classroom decisions. The findings underscore the pivotal role of critical reflection in teacher education programs and the need for thoughtful practicum placements. Further discussions provide implications and recommendations for teacher education research and practice.