School desegregation has been promoted as a means for decreasing racial hostility and for raising minority achievement. A study was conducted to explore the effects of school organizational structure on the race/gender composition of interacting social networks of adolescents attending two middle schools. While the schools varied in the opportunities provided for interactions among classmates, each had a student body similar in socioeconomic status and percentages of white and black students. Middle School (MS) had interdisciplinary, multigrade team organization with random assignment of students resulting in a heterogeneous student population. Junior High (JH) had ability tracking with limited student interaction. Data were collected from 345 seventh graders at JH and 332 seventh graders at MS. Students rated how often they talked with all other students in their grade. Factor analysis was used to describe the social networks existing at each of the schools. By controlling opportunities for interactions, school structure was found to affect the size, race, and gender of social groups and linkages between them. The results indicated that: (1) black males were better represented in white social networks at MS than at JH; (2) black females were equally accepted in both schools; and (3) acceptance of whites by blacks was generally better at MS than at JH. These results suggest that a school's structure is important in fostering interracial relationships. References and data tables are appended. (Author/NRB)