This study examined the effect of Activity-Based Teaching Strategy on Secondary School Students' Academic Performance in Mathematics in Ilorin, Nigeria. 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 Activity-Based Teaching Strategy and those taught with conventional method. The findings of the study showed that: (i) experimental group in private school had the mean score of ( = 15.00) while the counterpart in the control group had the mean score of ( = 13.25); (ii) 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 concept with activity-based method 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. It is recommended that Mathematics teachers should be trained to update their knowledge in the use of activity-based teaching strategy for making the teaching and learning of Mathematics more interactive and interesting.