Study of horizontal organization of secondary education is concerned principally with two classes of education at that level. In the first place it deals with all types of specialized education, whether found in special curriculums such as college preparatory and industrial arts in comprehensive schools, or in special schools, each emphasizing academic work, commercial subjects, manual arts, trades, or some other field. In the second place it deals with part-time education exemplified in the continuation and evening school. This monograph contains the following chapters: (1) The Problem of Horizontal organization; (2) Programs of different types of secondary schools; (3) Part-time cooperative curriculums; (4) The guidance of pupils in comprehensive and specialized school systems; (5) The Proximity of residence of pupils to secondary schools; (6) Characteristics of pupils in various curriculums and schools; (7) Attitudes and association of academic and vocational pupils; (8) Educational and vocational activities of former pupils; (9) Correspondence courses in public secondary schools; (10) The Summer high schools; and (11) The evidence and the issues. Individual chapters contain footnotes. (Contains 84 tables and 10 figures.) [Best copy available has been provided.].