<p>This study investigated the effects of activity-based instructional strategy on senior secondary schools students’ retention in circle geometry. The study employed a quasi-experimental design of the type pre-test, post-test groups design. The sample for the study comprised of 162 senior secondary 2 students drawn from two randomly selected co-educational schools in Federal Capital Territory, Nigeria. The research instrument was Mathematics Retention Test (MRT) containing items adapted from standardized WAEC questions. The test –retest method was employed for the reliability of the test instrument. The Pearson Product Moment Correlation Coefficient (r)=0.86 was obtained. Data collected were analyzed using t-test. The finding of this study revealed that there was a significant difference in the retention of students taught circle geometry using activity-based instructional strategy (ABIS) and the students taught circle geometry using conventional methods in favour of the students taught using ABIS. The study also indicated that there was no significant difference between the retention of male and female students in the experimental group who were taught circle geometry using ABIS. It was therefore recommended that mathematics teachers should use strategies that will encourage the active participation of students in mathematics classes such as ABIS which in turn would enhance retention. Also, governments at all levels should organize trainings and/or workshops for mathematics teachers on the use of ABIS in teaching mathematics.</p><p> </p><p><strong> Article visualizations:</strong></p><p><img src="/-counters-/edu_01/0873/a.php" alt="Hit counter" /></p>