Teaching mathematics as a STEM subject in this 21<sup>st</sup> century must be challenging enough to inspire learning, especially in the basic schools. This also depends on the pedagogical content knowledge and skills of the teachers handling the subject. Therefore, there is a need to design modern instructional strategies for training future teachers handling the pupils at the primary schools. Flipped classroom approach is one of the emerging pedagogical strategies that has proven to be very efficacious in teaching almost all subjects. Therefore, this research aimed to investigate the impact of flipped classrooms as a pedagogy in equipping the pre-service teachers with the knowledge and concepts of plane geometry, which happens to be one of the main branches of mathematics. A sample of 101 basic school pre-service teachers was purposively sampled for the study. A pre- and post-test design were used to gather quantitative data for analysis using a quasi-experimental approach. Based on the analysis of the results, the null hypothesis was rejected since there was a statistically significant difference in the pre-service teachers’ performance before and after the intervention. The study concluded that there was an improvement in performance due to the intervention. Therefore, the researcher recommends the flipped classroom approach as a formidable pedagogy for teaching pre-service teachers.