In recent years, over 1,000 middle schools of varying grade level organization have been established in 49 States. From an intensive study of materials published between 1961 and 1968 (listed in an appended bibliography), a basic rationale has been developed for the momentum of this trend. The new concept of the middle school (grades 6-8) is viewed as effectively meeting the particular needs of today's youth, who mature physically, emotionally, intellectually, and socially much earlier than did their counterparts at the turn of the century when the junior high school (grades 7-9) was introduced. An ESEA Title III planning project led to the recommendation that the Albuquerque Public Schools move to a 5-3-4 grade level organization, incorporating a middle school for grades 6-8. (JK)