The allure of using data to improve performance is a source of tremendous activity in the education field today. "Data use" has spurred a wide variety of reforms at all different levels of the education system, ranging from infrastructure augmentation to state databases, to district dashboard systems that collect and display an array of indicators, to the formation of school data teams that conduct data-informed inquiries into subgroups of students, to specific formative assessment classroom techniques. From this cornucopia it is increasingly apparent that data use means different things to decision-makers at different levels of the education system, and that the type of data, frequency of the data, mode of inquiry, and decision-making processes look quite different from one another according to role, situation, and purpose (Supovitz & Klein, 2003; others). Thus, when we talk about the term "data use," we must hone in on "for whom?" and "for what purpose?" In this paper, the author is interested in what it means for teachers to fruitfully use data to enhance the teaching and learning process. Informed by research on the challenges teachers face to use data meaningfully, and clues from the rich literature on formative assessment, this paper reports on the design and effects of an intervention designed to help teachers connect data on their teaching with data on the learning of their students for the purpose of informing subsequent instruction which leads to better student outcomes. The hypothesis of this study, therefore, is that while examining data may be useful, the real value of data use is to examine the connection between data points--in this case the instructional choices that teachers make and the learning outcomes of students. Thus, "data use" in this study means encouraging and facilitating teachers' analytical experiences of linking data on teaching to data on the learning of their students. Using a randomized control trial, the Linking Study tests the impacts of the intervention on teachers' perceptions of their fluency with data and their self-reported learning about their instructional practices and their students' thinking. Moreover, the study estimates effects on instruction caused by the intervention, based upon external trained raters' judgments of the quality of instructional practice. Finally, this research examines impacts of the intervention on student outcomes. Appended is: Survey Items and Scale Reliabilities.