This case study investigated gender-based differences in classroom participation through examining teacher-student interactions between a female biology teacher and two groups of middle school students, namely high achievers and low achievers. The female teacher used a questioning-orientated instructional strategy as her major teaching style which creates greater opportunities for student participation in biology learning. Classroom sessions were videotaped for one school year, then analysed for gender differences in question-and-answer patterns. The results showed that more teacher-initiated questions, teacher-directed interactions, and teacher feedback were given to males than females in both groups, but a large difference was found between the two groups of students. Girls in the low-achieving biology class (LABC) were more likely to participate at a rate comparable with their male classmates; girls answered more procedure questions and an equal percentage of process questions, called out approximately the same percentage of answers to undirected teacher-initiated questions, and received more instances of praise and follow-up questions. Contrary to what was observed in the high-achieving biology class (HABC), LABC girls initiated more questions than LABC boys.