Efforts to segregate disruptive students from the general school population have been tried repeatedly in the city, with mixed results.

Through the mid-1970's, the city had so-called "600 schools.

In the early 1980's, for example, Chancellor Frank J. Macchiarola created Outreach Centers which came to serve as temporary placements for suspended students and permanent assignments for some.

Joseph A. Fernandez called them Borough Academies, four schools for violent students that he created in 1992.

Ramon C. Cortines called them Crossroads Academies, for students caught with weapons, a program created in 1995.

Rudy Crew called them Second Opportunity Schools, intended for the 300 most violent students, a program created in 1997.

Chancellor Joel I. Klein called them New Beginnings centers, off-site programs for repeat offenders of the discipline code, centers that he and Mr. Bloomberg created last year. (Originally, they were called Twilight schools, until officials recognized the unfortunate connotation of troubled students being sent into oblivion.)