© 2021 Taylor & Francis Group, LLC.Low-achieving adolescents are known to have difficulties with reading comprehension. This article discusses whether principles of reciprocal teaching can improve low-achieving adolescents' reading comprehension in whole-classroom settings and to what extent treatment effects are dependent on implementation quality. Over the course of two years, experimental teachers (n = 10) were given training and coaching aimed at using principles of reciprocal teaching, while control teachers (n = 10) used their regular teaching method. Observations of teacher implementation were focused on instruction of reading strategies, modeling, and support of group work, and were performed in both experimental and control classes, comprising a total of 238 students (grade 7). The study shows that overall, there is no effect of the treatment on adolescent low-achievers' reading comprehension. Interestingly however, the principle of modeling positively moderated the effect of reciprocal teaching In addition, results suggest that the quality of implementation of reciprocal teaching in whole-classroom settings should receive more attention.