Background: Considering the significant impact of school-based HIV/AIDS education, in 2007, a curriulum on HIV/AIDS was incorporated in the national curriculum for high school students of Bangladesh through the Government’s HIV-prevention program. Based on the curriculum, an intervention was designed to train teachers responsible for teaching HIV/AIDS in classes. Methods: In-depth interviews were conducted with teachers to understand their ability, skills, and confidence in conducting HIV/AIDS classes. Focus-group discussions (FGDs) were conducted with students who participated in HIV/AIDS classes. HIV/AIDS classes were also observed in randomly-selected schools. Thematic assessment was made to analyze data. Results: The findings showed that the trained teachers were more comfortable in using interactive teaching methods and in explaining sensitive issues to their students in HIV/AIDS classes. They were also competent in using interactive teaching methods and could ensure the participation of students in HIV/AIDS classes. Conclusions: The findings suggest that cascading training may be scaled up as it helped increase ability, skills, and confidence of teachers to successfully conduct HIV/AIDS classes.