This longitudinal study measured the impact of pubertal development, sex, race, and school type on the self-esteem of 12- and 13-year-old children. One of the questions being investigated was whether the move from a protected elementary school into a larger, more impersonal junior high affected children's self-image more negatively than did a move from 6th to 7th grade within the same school. Subjects were 798 children from 18 elementary schools who were interviewed privately once in 6th grade and a year later in 7th grade. There were three main school populations in the sample: (1) K-8 schools, (2) K-6/ junior high schools with comparable social characteristics, and (3) K-6 junior high schools which were predominately black. The interview consisted primarily of multiple choice questions concerning self-esteem, social and school behavior. Results indicated that white girls scored lower in self-esteem than black girls or white and black boys. An analysis of the data comparing white students in K-8 schools with those in K-6/junior high programs indicated that girls moving into a junior high school were more likely to show low self-esteem than girls remaining in a K-8 system. Boys did not appear to be affected by school type. Maturation (as measured by the presence of menstruation), achievement scores and dating behavior also affected self-esteem in girls. Results are discussed. (SB)