CHICAGO - The Chicago Public Schools have given dismissal notices to some 775 probationary teachers, school officials said Friday.

District leaders said the purge is part of a move to improve the quality of instruction in the system's most challenged schools.

School Superintendent Arne Duncan told the Chicago Tribune that the cuts allow principals to build the best teams for their schools. Duncan denied that they were being made to solve budget problems or get rid of outspoken teachers.

The teachers were dismissed for various reasons, but the most common was an inability to manage their classrooms. Probationary teachers include those who have been in the district less than five years and others who have worked for longer than that as full-time substitutes.

The cuts represent about 11 percent of the district's estimated 7,000 non-tenured teachers.

Principals always have had the right to dismiss teachers who have been in the district fewer than five years, but the current contract with the Chicago Teachers Union makes the process easier.