Mathematics has be stereotyped as a male-dominated subject, and there is considerable evidence to support this belief. There has been much research in the past three decades on gender-related differences in elementary and secondary school mathematics. The research found that teachers possess different beliefs about male and female students that influence their teaching behaviour, which then directly or indirectly impact their students' behaviours, beliefs, and achievements in mathematics. Based on data collected from teacher questionnaire surveys in the Chinese Mainland and Hong Kong, this study examines teachers' beliefs about the achievements of boys and girls in mathematics. The study also compares the findings in the two regions surveyed. Results showed that teachers gave more attention to boys than girls, regardless of the teacher's gender. Not only are teachers more likely to recall more boys than girls, but also more boys than girls with average academic standards. Copyright © 2013 Korean Society of Mathematical Education.