Monitoring learning progress enables teachers to address students' interindividual differences and to adapt instruction to students' needs. We investigated whether using learning progress assessment (LPA) or using a combination of LPA and prepared material to help teachers implement assessment-based differentiated instruction resulted in improved reading skills for students. The study was conducted in second-grade classrooms in general primary education, and participants (N = 33 teachers and N = 619 students) were assigned to one of three conditions: a control group (CG); a first intervention group (LPA), which received LPA only; or a second intervention group (LPA-RS), which received a combination of LPA and material for differentiated reading instruction (the "reading sportsman"). At the beginning and the end of one school year, students' reading fluency and reading comprehension were assessed. Compared with business-as-usual reading instruction (the CG), providing teachers with LPA or both LPA and prepared material did not lead to higher gains in reading competence. Furthermore, no significant differences between the LPA and LPA-RS conditions were found. Corresponding analyses for lower- and higher-achieving students also revealed no differences between the treatment groups. Results are discussed regarding the implementation of LPA and reading instruction in general education.