This thesis explores impact of evidence-based active-engagement courses (EBAE) on student achievement and gender gap in introductory physics. The first study is about the pedagogical content knowledge (PCK) of the physics teaching assistants (TAs) at identifying introductory students' difficulties using the Conceptual Survey of Electricity and Magnetism, which is important for implementing evidence-based pedagogy. The second study focuses on EBAE physics classes in which there are potential opportunities for instructors and TAs to apply their PCK and other research-based instructional strategies to improve student learning. We investigated whether EBAE classes improved student performance compared to traditional lecture-lased (LB) classes and whether EBAE classes helped improve student performance. Our findings suggest that, on average, students in EBAE classes outperformed students in LB classes in conceptual post-tests although their scores on pretests were not statistically significantly different. Moreover, on average, both male and female students in EBAE classes outperformed those of the same gender in LB classes on post-tests although there was no difference on the pretests. However, no reduction in the gender gap in EBAE classes was observed.

We also investigated the impact of stereotype threat in introductory physics classes. When students were asked to indicate their gender immediately before taking standardized physics tests, no deterioration in female students' performance on standardized test was observed compared to the case when gender was not indicated. Moreover, we also investigated the extent to which agreeing with the stereotype that men to generally perform better in physics than women was correlated with students' performance and found that this type of belief is not very common(~10%). However, in some situations, female students who agreed with the stereotype performed worse than female students who did not agree with it.