In this study, poor readers in second school year were selected from three schools (n = 32). Their reading skills were surveyed weekly using a CBM instrument over one school semester. Furthermore, they were supported by a five-week reading fluency instruction. The majority of students increased their weekly learning growth in regular teaching and in the phase with the additive instruction. The weekly learning growth was higher in the phase with the additive instruction in reading syllables (b = 0.69), reading words (b = 0.44) and reading comprehension at sentence level (b = 0.45) than without (reading syllables: b = 0.49; reading words: b = 0.18; reading comprehension: b = 0.30). Based on the results of this study, the benefit of CBM for adaptive reading instruction will be discussed.