The relationship between within-class reading grouping and self-concept was investigated in a sample of 257 third-grade children in 12 classes that employed within-class grouping. Pupils were tested at the beginning and end of the school year, using the Piers-Harris Test, a semantic differential, and an inventory containing four items about competitiveness. Results indicated that there were significant differences in self-concept among high, middle, and low reading groups. Significant differences in the amount of change in self-concept in the three groups were found over the school year on the semantic differential but not on the Piers-Harris Test. Feelings of competitiveness were expressed most frequently by the high group, not as frequently by the middle group, and least by the low group. Children who moved to a higher reading group showed significant increase in self-concept on the Piers-Harris Test, but not on the semantic differential. (Author/AA)