By Alice Popovici BALTIMORE (Reuters) - The U.S. Justice and Education departments unveiled guidelines on Wednesday to prevent schools from violating civil rights laws and keep students out of jail after data found minorities and the disabled were more likely than others to face discipline or arrest. Attorney General Eric Holder said the guidelines were aimed at giving direction to school law enforcement officers, protecting the civil rights of students, and disrupting what he called "the school-to-prison pipeline." Effective discipline is, and always will be, a necessity. But a routine school discipline infraction should land a student in a principal's office - not in a police precinct," Holder, joined by Education Secretary Arne Duncan, said after meeting students at Baltimore's Frederick Douglass High School. He said many students were suspended, expelled or arrested for minor lapses such as school uniform violations, schoolyard fights or laughing in class. Black students and those with disabilities often received different and more severe punishment than others, Holder said. The guidelines came after the Justice Department sued Mississippi state and local officials in 2012, saying they violated the rights of children, especially black and disabled youths. The American Civil Liberties Union and the NAACP Legal Defense and Educational Fund applauded the guidance as recognition that racial discrimination was a problem in school discipline. "This is a victory for all who care about creating environments where students can thrive," Deborah Vagins, the ACLU's senior legislative counsel, said in a statement. Additional reporting by Ian Simpson; Editing by Daniel Trotta, Ken Wills and Bernard Orr