This study investigated gender inequality in biology lessons and analysed the effects of the observed inequality on students' short-term knowledge achievement, situational interest and students' evaluation of teaching (SET). Twenty-two biology teachers and 803 7th-grade students from rural and urban classrooms in China participated in the study. Each teacher was videotaped for 1 lesson on the topic "blood and circulatory system." Before and after the lessons, the students completed tests and questionnaires. Chi-square analysis was conducted to compare the boys' and girls' participation rates of answering teachers' questions in the lessons. The findings revealed that in the urban classrooms the boys had a significantly higher rate of participation than did the girls, and hence also a higher situational interest. However, no such gender inequity was found among the rural students. The study also revealed that urban students answered more complicated questions compared with the rural students in general. The findings of this study suggest that the teachers should try to balance boys' and girls' participation and involve more students in answering questions in their lessons. The study also raises questions about long-term effects of students' participation in answering teachers' questions on their outcomes-knowledge achievement, situational interest and SET.