"Castañeda v. Pickard" mandated that educational programs for emergent bilinguals be tested for program efficacy. As English language development (ELD) curricular materials are one part of an instructional program, we assess this mandate by examining the effectiveness of ELD materials in Texas, a large, diverse U.S. state with large numbers of emergent bilingual (EB) students. Using local linear matching, we find robust evidence that schools that do not purchase any ELD curricula have significantly lower English language proficiency scores relative to schools that purchase state-adopted ELD materials. In contrast, there is no significant difference between schools that adopt the two most popular ELD curricula in the state. This study suggests that curriculum materials matter for EBs' English proficiency and implies that states should take a more active role in ensuring students have access to these materials.