Sub-Saharan Africa has been severely affected by HIV and AIDS. Kenya's education sector, aiming to protect learners from HIV infection, has developed the Education Sector Policy on HIV and AIDS and an HIV/AIDS curriculum. This policy mandates the incorporation of HIV/AIDS information in curricula and extra-curricular activities in learning institutions, including primary schools, by teachers. The goal of this dissertation study was to investigate the factors influencing teachers' implementation of classroom-based HIV/AIDS education in rural, public, mixed, day, primary schools in Kakamega Central, East, North, and South districts in Kenya. A mixed-methods approach was applied, combining quantitative and qualitative methods and techniques. A self-administered survey was conducted of 516 teachers in 40 primary schools in the four districts, with a 92 percent response. Survey data was analyzed using structural equation modeling. The independent variables included teachers' attitudes and beliefs derived from the constructs of the Theory of Planned Behavior (TPB) framework that guided the study. These constructs were teacher attitude, subjective norms, and perceived behavioral control. Variables external to the theory—teacher training in HIV/AIDS education and the class level taught—were also examined. Qualitative data was collected from interviews of teachers in two schools that had participated in the quantitative part of the study; the data was analyzed using an ethnographic approach. Quantitative findings showed that teachers' in-service training in HIV/AIDS education, attitudes, and class level taught, and their perceived behavioral control had an effect on their implementation of classroom-based HIV/AIDS education. The qualitative results were consistent with these findings. The study's findings have several policy implications in terms of the significance and value of teacher training and teachers' access to knowledge and resources in relation to teaching HIV/AIDS education in the classroom.