Low-achieving adolescents are known to have difficulties with reading comprehension. This article discusses how reciprocal teaching can improve low-achieving adolescents' reading comprehension in whole-classroom settings (as opposed to small-group settings) and to what extent intervention effects are dependent on teacher behaviour. Over the course of 1 year, experimental teachers (n = 10) were given extensive training and coaching aimed at using principles of reciprocal teaching, while control teachers (n = 10) used their regular teaching method. Observations of teacher behaviour were focused on instruction of reading strategies, modelling and support of group work and were performed in both experimental and control classes, comprising a total of 369 students (mean age = 13.01). Our study shows that reciprocal teaching contributed to adolescent low achievers' reading comprehension only when experimental teachers provided high-quality strategy instruction. In addition, results suggest that the quality of implementation of reciprocal teaching in whole-classroom settings should receive more research attention. Highlights: What is already known about this topic Reciprocal teaching is a method of instructing and guiding learners in reading comprehension. It consists of a set of three related instructional principles: (a) teaching comprehension-fostering reading strategies; (b) expert modelling, scaffolding and fading; and (c) students practising and discussing reading strategies with other students, guided and coached by the teacher. High quality of implementation of reciprocal teaching by teachers in classrooms is difficult. What this paper adds After 1 year of implementing reciprocal teaching, no main effects of the treatment were established. Intervention effects were moderated by quality of instruction: strategy instruction led to higher scores on reading comprehension in the treatment condition but not in the control condition. Implementation of the instructional principles was by no means optimal: teachers were unable to provide detailed guidance to students working in small groups and modelling of strategies requires more experience and theoretical insight in the use and nature of reading strategies. Implications for practice and/or policy Extensive training and coaching are needed for teachers to become experts in reciprocal teaching. Teachers need hands-on tools to be able to guide students in their collaborative group work and to fade the teachers' role in order to allow more individual self-regulation by students in their use of strategies. Implementation quality has to be taken into account when doing effectiveness research and when adopting new, theory-based didactic approaches.