Large-scale summative assessment results are typically used for program-evaluation and resource-allocation purposes; however, stakeholders increasingly desire results from large-scale K-12 assessments that inform instruction. Because large-scale summative results are usually delivered after the end of the school year, teacher use of results is reserved for the subsequent academic year. To evaluate use of summative score reports to inform instruction, we conducted a series of teacher interviews and focus groups with 17 teachers in three states. Teachers were asked to describe how they used summative results from the previous administration of a large-scale alternate assessment system in the subsequent academic year. Interview and focus-group transcripts were coded and identified themes related to when and how score reports are delivered; how teachers use results to plan instruction, formulate goals for individualized education programs (IEPs), and create instructional groupings; how teachers talk to parents about results; and what resources best support their use of score reports. Findings demonstrate preliminary support for diagnostic score report use.