AbstractSeveral studies have shown that using mind mapping as an approach to teaching Mathematics has a more positive impact on student achievement than traditional approaches. However, these studies did not address the effect of mind mapping in other countries, such as Nigeria, at a secondary school level; they focused more on digital mind_mapping for pre-service teachers. This study examined how students' mathematics achievement in Ogun State, Nigeria, was affected by the mind mapping instructional technique. Nonrandomized pre-test post-test control group design, or quasi-experimental non-equivalent group research design, was used. A simple random sample technique was used to assign one school to the experimental group and another school to the control group. The data required for the study was collected using the Mathematics Achievement Test, which has a reliability coefficient of 0.87 according to the Kuder-Richardson formula 20 (KR20). Four hypotheses were tested at the 0.05 significant l.....