We examine how teacher leaders (TLs), working in a low-income urban elementary school, supported their colleagues to learn how to collect quality formative data and to discuss it in collaborative conversations in order to make their students' learning visible. The TLs faced challenges reflecting consequences resulting from the district's high stakes accountability policies restricting teachers' agency with instructional decision-making and limiting their definitions of data as summative test scores. We document how the TLs worked to reframe teachers' understanding of data to include evidence of student thinking and supported their colleagues to reclaim teaching as professional versus technical work.