This study investigated preservice teachers from two teacher education programs, elementary generalists and bilingual generalists (who will teach all subjects in both English and Spanish), about their instructional design abilities via examination of their ability to integrate interdisciplinary-themed activities into mathematics lessons. The findings illustrate the value provided by differentiating teacher preparation for preservice bilingual teachers--especially for challenging STEM-related (science, technology, engineering, and mathematics) subjects such as mathematics--based on their distinctive pedagogical, cognitive, and linguistic requirements.