Learning trajectories (LTs) hold promise to effectively convey to teachers significant patterns in student thinking. The research on learning that undergirds LTs has accumulated over several years, and the research base continues to develop. However, most of this research is not easily accessible–much less actionable–by most teachers. We introduce a digital learning system (dls), based on LTs, as a means of providing teachers systematic access to information on student learning. In particular, we illustrate the use of this system’s LT-aligned diagnostic assessments, on percents, to provide valid and timely data to teachers and students alike. The DLS itself tracks student progress over time, and data from field testing supports research on the refinement of the trajectories and their measures.