In 1965, queries sent by the Educational Research Service (ERS) to 461 school systems identified only 63 middle schools concentrated in 20 systems. Only 13 of these 20 systems enrolled more than 12,000 pupils. When school systems of similar size were again polled at the opening of the 1968-69 school year, 70 systems reported 235 middle schools. This growth in the number of middle schools in the past 4 years prompted this detailed report on the characteristics of each individual school. Information for each school includes: (1) Identification of the school system and the name of the school, (2) first year operated, (3) grades included, (4) number of students, (5) number of staff positions, (6) ability grouping, (7) instructional practices, (8) subjects taught by teams, (9) special subjects--both required and elective, and (10) activities. Special comments by principals of middle schools, an index to school systems with middle schools, a bibliography of 15 books and pamphlets and 26 articles, and a sample questionnaire are also included. (DE)