"Castañeda v. Pickard" established a precedent for evaluating bilingual programs in relation to the "soundness" of the educational theory on which they are based. However, this notion of theoretical soundness was grounded in an underlying logic that ultimately framed emergent multilingual students as a "protected" class--or vulnerable population in need of Federal protection. Given the particular demographic context in which the "Castañeda" case emerged, this population of students was also imagined to be primarily Latinx, a category which, in turn, was imagined to exclude Black students. In this article, we interrogate this underlying logic, and we propose an expanded definition of what counts as sound theory in relation to bilingual education. In light of recent international attention to the Black Lives Matter movement, we explore the role of bilingual education in the lives of Black and Latinx students who attend schools with one another throughout the U.S. We argue that the "Castañeda" discourse that framed Latinx children's emergent multilingualism as "language barriers" was--and continues to be--informed by the same logic that frames Black kids as not being bilingual (and as not belonging in bilingual education). Further, we argue that this logic has profoundly shaped a history of language policies that are primarily remedial and compensatory in nature, and that systematically exclude and/or marginalize Black students. Through an interrogation and reimagining of "sound educational theory," we point to ways that bilingual education can encompass a more expansive view of multilingual learners that promotes linguistic solidarity between Black, Latinx, and other racialized students.