Physics students’ poor retention culminates in poor achievement owing to teaching methods that are unrelated to their culture. This study determined the effectiveness of the ethnoscience-based teaching method on student retention in Optics by adopting a non-equivalent control group design on 160 students. The experimental class was taught rectilinear propagation of light using the ethnoscience-based teaching 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< .05). The results indicated a higher retention for the use of the ethnoscience-based teaching method than the lecture method, while there was no significant gender-based factor in the students’ performance. The use of the ethnoscience-based teaching method could transform science teaching, enhance students’ construction of new science concepts based on their existing knowledge and bridge the gap between Western science and students’ world views.