Teachers must be proficient at using data to evaluate the effects of instructional strategies and interventions, and must be able to make, describe, justify, and validate their data-based instructional decisions to parents, students, and educational colleagues. An important related skill is the ability to accurately read and interpret progress-monitoring graphs. This study examined preservice special education teachers’ graph reading and interpretation skills at two points in time. Participants used a think-aloud procedure to interpret a curriculum-based measurement (CBM) progress monitoring graph, and results were compared to those of CBM experts. Overall, preservice teachers tended to say fewer words than graph experts did. Furthermore, their descriptions of CBM graphs were less sequentially coherent, specific, and reflective. Little change was observed at time 2. Implications for improving teacher preparation in this skill area are discussed.