The purpose of this study was to examine the effects of homogeneous versus heterogeneous ability grouping on performance and attitudes of students working cooperatively on master learning during back-hand squash instruction. The participants were 80 undergraduate students, classified as high and low ability skill randomly sampled from the physical activities program. Equal number of participants were randomly assigned to treatment, stratified for ability and gender. The study employed a 2 by 2 randomised block design. The first factor was the type of grouping (heterogeneous versus homogeneous), and the second ability (high versus low). The department variables were achievement and attitudes. Two way ANOVA results yielded a significant main effect for student ability, F (1.76) = 28.30, p< .001. The main effect for type of grouping, on the other hand, was not significant, F (1.76) = 3.18, p = .086. The interaction between ability and group composition was also significant, F (1.76) = 6.82, p= .016. In addition, the mean attitude score for low ability students was higher than the mean attitude score for high ability students. Similarly, heterogeneous ability grouping resulted in higher mean attitude score than homogeneous grouping. Results of this study showed that heterogeneous ability grouping was effective for all students, regardless of their ability levels. There was no statistically significant difference in the performance of high-ability students in either group. However, homogeneous ability grouping was detrimental for the achievement of low-ability students. This is consistent with the findings of some other studies. One possible explanation for this result would be that homogeneously grouped low ability students may not be capable of supporting each other's learning needs. In addition, the results revealed that heterogeneous ability grouping generates more positive attitudes toward instructional system. Perhaps, low-ability students in heterogeneous groups feel more supported and satisfied than other students. One of the potential variables that should be investigated thoroughly is the impact of exercising cooperative structure during mastering learning work. Future research should also examine the effects of motivational factors during the instruction.