Physics students' poor retention culminates in poor achievement owing to teaching methods unrelated to their culture. This study aimed to determine the effectiveness of the ethnoscience-based teaching (EBT) method on student retention in optics by adopting a non-equivalent control group design involving 160 students. The experimental class was taught rectilinear propagation of light using the EBT method, while the control class was taught the same topic using the lecture method. The collected data were analysed using arithmetic mean and analysis of covariance (p < 0.05). The results indicated a higher retention level among participants who were taught using the EBT method compared with the lecture method. At the same time, there was no significant sex-based factor in the participants' performance. The use of the EBT method has implications for physics teaching, that is, it can transform science teaching and enhance students' construction of science concepts based on their existing cultural knowledge instead of clinging to Western cultural orientations. Therefore, EBT should be integrated into physics teaching as it can be taught in a way related to nature as perceived from the students' world-views.