The problem of this investigation was to determine whether the association and competition between boys and girls during the crucial junior high school years resulted in significant differences in the development of boys. Five null hypotheses were proposed within the general problem: Are academic achievement, self-discipline, self-concept, sex-role identification, and attitude toward school (authority) different for junior high boys and girls who are grouped by sex, as opposed to those grouped together? A total of 300 students participated in this study. Conclusions drawn from this study include that all five of the null hypotheses tested by the study were supported by the treatment of analysis of covariance. The few significant differences attributed to the interaction of the dependent variables and the grouping effect were judged to be spurious. The findings were that girls in general have a more positive attitude toward school, receive better grades and achieve higher in school studies related to language arts, irrespective of age, grade, or assigned group. (Author/KJ)