Students with extensive support needs (ESN), most of whom are taught in separate settings by special educators without extensive academic preparation, have difficulty making progress in the general education curriculum. Although there is evidence that data-based decision-making improves achievement for a wide range of students, there is little research on teachers' data use for academic instruction of students with ESN. In this study based on 403 survey responses from teachers in nine states, we examined the types of data that were available, how teachers perceived and used data, and how their perceptions were related to data use. Respondents more often reported having access to teacher-developed data sources than to external data (e.g. published assessments, local assessments). Even when external data sources were available, respondents more often used teacher-developed data. Respondents most often reported using data to set goals and tailor instruction, and least often to group students. Attitudes toward data and perceptions of personal data competence were positively associated with data use. School leadership and organizational supports were associated only with decisions about grouping students. There were group differences in data use depending on the type of data they perceived as useful.