This study examined the effect of peer assisted co-operative instructional strategy on the ability levels of students. Two research questions and hypotheses were developed to guide the study. A non-randomized pre-test and post -test control group design was adopted for the study. A total of 110 Senior Secondary 2 Chemistry students were used. Cognitive Ability Test (CAT) and Chemistry Performance Test (CPT) were the instruments used to generate data. Reliability coefficients of 0.82 and 0.80 were obtained for CAT and CPT respectively using Kuder-Richardson formula 21. Data collected were analyzed using descriptive statistics of mean, standard deviation, independent t-test and analysis of co-variance. From the findings of the study, it was observed that peer assisted co-operative instructional strategy had effect on cognitive ability levels of chemistry students. The result also showed that there was no significant difference existing among the academic performance of male and female students taught with peer assisted co-operative instructional strategy. Recommendations included that teachers should vary their instructional strategy to meet with students’ learning styles and cognitive ability levels instead of relying on the conventional method alone.
Key words: Peer assisted, cooperative instructional strategy, cognitive ability levels.