This report describes the intermediate school experiment which organized the middle schools to include grades 5 or 6 through 8, thus replacing the junior high school, grades 7 through 9. Major curriculum innovations were introduced in the areas of foreign language, the humanities, family living, typewriting, and creative and performing arts. The organization of these experimental middle schools embraced subschools, educational planning teams, departmentalization, and independent pupil study. Using the results from standardized achievement tests, an attitude inventory, a semantic differential, questionnaires, extended observation by consultants, and interviews, the research team compared middle school pupils with junior high pupils in the areas of mathematics achievement, attitudes toward school, and self-concept. The only statistically significant differences (analysis of variance) showed that junior high pupils performed better in arithmetic problem solving, while intermediate school boys had more favorable attitudes toward social studies and science. Appendixes include questionnaires and evaluation and survey forms used in assessing the program. (Author)