In the accountability era, educators are pressed to use evidence-based practice. In this comparative case study, we examine the learning opportunities afforded by teachers' data use conversations. Using situated discourse analysis, we compare two middle school mathematics teacher workgroups interpreting data from the same district assessment. Despite similarities in their contexts, the workgroups invoked different data use logics that shaped teachers' learning opportunities. The first workgroup's instructional management logic linked increasing student achievement to individualization. The second workgroup's instructional improvement logic focused on students' thinking and linked it to instructional changes but was limited by broader instructional management logics. Evidence-based practice cannot be understood apart from the data use logics in teachers' communities, which are shaped by policy constraints.