The major focus of this study is to propose a new research model, namely the Modified CGI gender model, for the study of gender differences in mathematics. This model is developed based on Fennema, Carpenter, and Peterson's (1989) CGI model. To examine the validity of this new model, this study also examines the gender differences in teacher and student beliefs about mathematics and compares gender differences between teacher and student beliefs about the importance and difficulty of certain mathematics topics. Using the British Columbia Mathematics Assessment data, the study conducted a series of ANOVA. The findings of this study indicate that the new model appears to be a useful tool to describe gender differences in mathematics and to guide research in this area. The conclusions drawn from the data analysis show that male and female teachers differed significantly in their beliefs about Numbers and Operations. Male teachers perceived this topic to be more important than female teachers. Second, gender differences have been largely found in student beliefs about the difficulty of the selected topics. Finally, gender differences found in teacher beliefs are similar to the gender differences in student beliefs about the importance and difficulty of mathematics topics.