This article describes the findings of studies conducted on a large-scale, classroom-based performance assessment of literacy for the early grades designed to provide information that is useful for reporting, as well as teaching. Technical studies found the assessment to be a promising instrument that is reliable and valid. Follow-up studies of the assessment's use point to its positive impact on teachers' practice and on school and district policies. The studies' findings suggest that classroom-based performance assessment can be a viable accountability, as well as instructional, tool, capturing a range of students' abilities in a range of formats, and that use of such an assessment has the potential to enhance teachers' knowledge about literacy and their abilities to effectively support students' learning.