The present study aimed to compare the effectiveness of two types of cooperative learning groups used in reciprocal teaching (RT) classes (i.e. high-structured vs. low-structured groups) for enhancing students' reading comprehension. The participants were 235 Hong Kong Chinese Grade 6 students in nine classes. Reading comprehension tests and questionnaires were used to investigate students' reading comprehension, teachers' cognitive support and perceptions of cooperative learning. The findings indicate that high achievers from the low-structured RT group significantly outperformed high achievers from the high-structured RT group in post-test reading comprehension, whereas low achievers from the high-structured RT group significantly outperformed low achievers from the low-structured RT group in follow-up reading comprehension. Students from the high-structured RT group reported higher scores for their perceptions of cooperative learning than students from the low-structured RT group.