The objective of this study was to determine whether the incorporation of group work in a teaching intervention can effectively foster students' critical thinking skills. Building upon Kuhn's critical thinking model, the research involved comparison of pretest and post-test results for 140 secondary four (10th grade) students in Hong Kong on two measures of critical thinking ability and investigation of their engagement in argumentative dialogues. The findings illustrate the efficacy of group work, relative to whole-class instruction, in helping students develop critical thinking. In addition, the findings highlight the efficacious role of the teacher in breaking the deadlocks that may arise during small-group debates.