This study examined the effect of co-curricular activities on the academic achievement of secondary school students in Abbottabad, Pakistan. 200 students were divided into experimental and control groups. The experimental group participated in physical and non-physical co-curricular activities for 40 minutes daily for 12 weeks, while the control group did not. Pre- and post-tests were used to measure the students' academic achievement in mathematics and English. The results showed that the experimental groups performed significantly better than the control groups on the post-test in government boys' schools, government girls' schools, and private girls' schools, but not in private boys' schools. Thus, the study concluded that co-curricular activities can positively impact academic achievement,