This study investigated possible differences in reading achievement of first graders when grouped by sex. The study also explored whether these groups' attitudes toward school, learning, and new experiences varied and, if so, how this affected reading achievement. Children were placed in five classrooms: one class of boys, one of girls, and three of both girls and boys. Computation of various interactions between these groups led to these conclusions: (1) regardless of grouping, first grade girls appeared to achieve more highly in reading than boys; (2) the all-girl class achieved more highly in reading than girls in the mixed class; (3) the attitudes of the girls in the all-girl group were lower than the attitudes of both the girls in the mixed group and the boys in the all-boy class; (4) there was no significant advantage in reading achievement or attitude for homogeneously grouped boys compared to heterogeneously grouped boys. Since the achievement gains of the girls in the all-girl class did not compensate for their poor attitudes, this class was not continued the next year, but the all-boy class was continued. The author suggests that further investigation be pursued into the social dynamics of a first grade classroom and into what is measured by various reading tests. (Author/DI)