This study compares the impact of Assessment of Learning (AoL) and Assessment for Learning (AfL) on students' mathematics achievement. The quasi-experimental study, which was carried out in the Ekiti Central Local Government Area of Ekiti State, Nigeria, featured 140 seniors in secondary education out of the total population of 500 senior secondary school students, including 200 male and 300 female students from ten public secondary schools in the area. A multi-stage sampling procedure was employed; simple random sampling was also used to select four intact classes from these schools (two from each). One intact class was randomly assigned to the experimental group and the other to the control group. Well-structured items named Mathematics Achievement Test (MAT)was developed and used for data collection. The instrument's face validity was confirmed.The respondents were split into two groups: the experimental group received training in AfL practices, while the control group received training in AoL techniques. Math proficiency was assessed by pre-test and post-tests. Significant post-intervention gains were seen in the experimental group's scores, according to analysis with t-tests and ANCOVA; no significant gender differences were noted. The findings support previous research emphasizingAfL's beneficial effects at all educational levels and highlight how well it can improve mathematical understanding. These results emphasize the significance of using AfL techniques in instructionto enhance mathematics learning outcomes.