The junior high school, comprised of grades 7-9, was originally organized to meet the special needs of adolescent students. Current trends in school reorganization favor a middle school comprised of grades 6-8, raising the problem of where to place the ninth grade in the school organization. Assuming that ninth graders should be placed with students more nearly resembling themselves, a test was made of the research hypothesis that ninth grade students more nearly resemble tenth grade students than they do eighth grade students. From two suburban Missouri school districts, data were gathered relative to the physical, emotional, intellectual, and social maturity levels of eighth, ninth, and tenth grade students. Data analysis showed significant differences between eighth and ninth grade students in physical, intellectual, and emotional maturity. The only significant difference between ninth and tenth grade students was in physical maturity, since tenth graders were found to be more physically mature. The research hypothesis was therefore confirmed, leading to the conclusion that ninth graders would best be placed in senior high units rather than in junior high or middle school units. A 127-item bibliography of relevant literature is included. (EA)