With the goal of achieving bilingualism and biculturalism, dual language education (DL) has a social justice orientation. As the program option with the best track record of closing the achievement gap between Latinx and White students, DL programs can potentially create environments in which learners can develop knowledge of science, technology, engineering and mathematics (STEM) in two languages. In this article, we present findings from a two-year ethnographic study of engineering design curriculum in a K-5 DL program on the U.S.-Mexico border. Our team researched the implementation of a hands-on, highly interactive, inquiry-based STEM curriculum because immigrant emergent bilinguals from border communities are sometimes excluded from these learning opportunities. During the first year of implementation, the STEM curriculum was not taught following DL goals. Essential principles of DL education, including the use of two languages for instruction and equal status for both languages, were not followed. Lack of familiarity with the STEM curriculum and emerging expertise of engineering design explained this decision partially. Due to a dearth of resources, training, and expertise in engineering and in inquiry-based learning, the implementation failed to meet its counterhegemonic potential. In fact, it may have reproduced hegemonic practices that marginalized emergent bilingual Latinx students.