In most general education classrooms in Germany, students with and without special educational needs are taught together. To support teachers in adapting instruction to these heterogeneous classrooms, we have developed learning progress assessment (LPA) and reading instructional materials, the "Reading Sportsman" (RS), in line with the theoretical framework of data-based decision-making, which has led to beneficial effects in several studies. However, data from these studies have not been analyzed to examine effects for low-performing readers. Data within and across six quasi-experimental studies conducted by our team in Grades 2 to 4 were reanalyzed to examine the effects of LPA on students whose reading fluency scores were at or below the 25th percentile (n = 1,346 students from 264 classes). In each study, students had been assigned to a control group (with business-as-usual instruction), an LPA group only, or an LPA-RS group (i.e., with teachers provided with LPA and the RS). Separate multilevel regression results were integrated by means of meta-analytical methods to investigate the consistency of results. Overall, findings from the single studies indicated no positive effects of LPA with or without the RS compared with the control group. The integrated analyses showed small positive effect trends on reading fluency and intrinsic reading motivation.