More than a quarter of US children have at least one immigrant parent, but researchers and policymakers often do not have adequate data on these children's experiences in school, with far-reaching implications for instruction, student support services, and policy. Proxy factors that are reported by school--such as being designated as an English learner or data on race and ethnicity--can tell only part of the story for children of immigrants. This essay demonstrates the untapped value of data on languages spoken at home and explores how policymakers might rethink collection and use of data. Better data on student background can enhance the understanding of students' experiences and provide nuanced information to educators, researchers, and policymakers to better serve distinct student subgroups. The authors show that including data on languages spoken at home can help explain student academic test outcomes. In sum, data on languages spoken at home provide more nuanced and actionable information that can be used for decision-making.