In the decade since school districts instituted "zero tolerance" discipline policies, administrators have increasingly suspended minority students, predominantly for nonviolent offenses, according to a report released Wednesday.

The National Education Policy Center found that suspensions across the country are increasing for offenses such as dress code and cellphone violations. Researchers expressed concerns that the overuse of suspensions could lead to dropouts and even incarceration.

Suspensions are falling mostly on black students; nearly a third of black males in middle school have been suspended at least once, researchers from the University of Colorado-based group found.

In Los Angeles Unified, one of the school systems included in the report, district figures show a similar situation: Last school year, nearly 34% of students suspended from middle schools were