Learning progress assessment (LPA) provides formative information about effectiveness of instructional decisions. Learning curves are usually presented as graphical illustrations. However, little is known about teachers understanding and interpreting of graphically presented information. An instrument to measure competencies in reading graphs from learning progress assessment (LPA-test) was developed. One-hundred and twenty-four student teachers and 36 teachers completed the LPA-test and a second test that assessed reading graphical information from diagrams. In addition, interviews from 10 teachers provided information about thinking processes while dealing with graphs on learning progress information. Technical adequacy of the LPA-test proved to be satisfactory. Results in the LPA-test underline the capacity that most teachers generally have when learning graphing. Interviews reveal that teachers skip a thorough description of the graphical illustration, concentrate on marginal details, and tend to immediately transmit students' achievement into school grades without structuring information.