One way to address the leaking pipeline toward STEM-related careers (i.e., science, technology, engineering, and mathematics) is to intervene on students' STEM motivation in school. However, a neglected question in intervention research is how such interventions affect motivation in subjects not targeted by the intervention. This question was addressed through data from a cluster-randomized study in which a value intervention was successfully implemented in 82 ninth-grade math classrooms. Side effects on value, self-concept, and effort in German as students' native language and English as a foreign language were assessed 6 weeks and 5 months after the intervention. Negative effects on value for German, but not for English, were found 5 months after the intervention. The theoretical and educational implications of such effects are discussed.