This paper reports the findings of a quasi-experimental study that investigated the impacts of effective group work on Hong Kong science classrooms. One hundred and fifty-two Secondary 2 (or Grade 8) students from two schools participated in a teaching intervention (comprising 16 lessons) in which they studied the topic 'Making Use of Electricity' and resolved a series of related scientific inquiries. Informed by both the quantitative (i.e. diagnostic tests) and qualitative (i.e. science inquiry questions, audio-recordings of group discussions and focus-group interviews) results of the study, this paper reveals that effective group work can narrow the social and gender differences in Hong Kong students' science performance. Whilst a dynamic and respectful learning environment was found to help economically disadvantaged and female students to overcome such barriers to science learning as low self-esteem and high anxiety, a gender-balanced and socioeconomically diverse arrangement was found to be an important element of social group work practice. Finally, the study's broad implications for teacher and peer support for science teaching worldwide are also discussed.