Mathematics concepts cannot be well understood if students are not taught using an effective teaching method, and this can lead to poor academic performance. The teaching of mathematics in Nigeria has fewer hands-on activities that directly engage the students’ ability to think and solve problems, such as the activity-based method. Hence, this study examined the effect of Activity-Based Teaching Strategy on Secondary School Students’ Academic Performance in Mathematics in Ilorin South, Kwara State. Quasi-experimental research of non-equivalent control group design was employed for the study. This design was adopted to compare the performance of students who were taught Binary Numbers with an Activity-Based Teaching Strategy and those taught with the conventional method. The findings of the study showed that: (i) the experimental group in private school had a mean score of ( = 15.00) while the counterpart in the control group had a mean score of ( = 13.25); (ii) the experimental group in public school had the mean score of ( = 12.00) while the counterpart in the control group had the mean score of ( = 9.73); (iii) private school students performed better than public school students with the mean different of ( = 3.00) after been taught mathematics concept with activity-based method; (iv) there was no significant difference in the performance of male and female students taught mathematics concept using activity-based method. [.561 0.05]; and (v) there was a significant difference between the academic performance of students taught mathematics concepts with activity-based methods based on school ownership (.000 0.05). The study concluded that complex ideas in mathematics can be understood easily with the help of activity-based teaching.