Increased attention to Data-Informed Instruction (DII) and learning analytics has not been accompanied by a commensurate base of theory or evidence showing how practitioners successfully enact DII, or illustrating what the difficulties and contextual particularities of doing so involve (Coburn & Turner, 2012; Little, 2012; Spillane, 2012). While it is theoretically clear how data should aid classroom teaching (e.g., by illustrating students' conceptualizations of different topics), very little research has investigated how teachers transform data into insight and then insight into pedagogical action. This paper presents a case study of how two teachers used an online reading analysis support tool to access data about students' reading homework and how those teachers used what they noticed about students' thinking through that data to enact DII.