Maryland school officials approved sweeping changes to the state's discipline policy Tuesday, banning zero-tolerance approaches and requiring local school boards to emphasize rehabilitation over punishment.

In a unanimous preliminary vote, the State Board of Education emphasized that cutting down on expulsions and long-term suspensions would translate to more classroom time and higher achievement for students, the ultimate goal of the state's school system. The changes are subject to state review and public comment and will be put to a final vote next month.

"No student comes to school 'perfect,' academically or behaviorally. We do not throw away the imperfect or difficult students," the state board wrote in a report explaining the changes.

The board also directed the state's Education Department to identify local districts that disproportionately suspend and expel minority students, giving these systems one year to reduce the disparity and three years to eliminate it.

Additionally, the new policy would require school districts to complete investigations into long-term suspensions and expulsions within 10 days and compel teachers to provide students serving out-of-school suspensions with daily assignments for grades.

Maryland began seeking changes to its discipline policy in 2009, when school leaders learned of a ninth-grader who received intermittent homework but no grading or other interactions with teachers while expelled for most of a school year.

"I don't think it was anything more than a lack of focus and lack of attention" that kept school leaders from revising the discipline policy before 2009, Board President James H. DeGraffenreidt Jr. told The Washington Examiner.

In the 2010-2011 school year, 8 percent of Maryland students were suspended or expelled. More than half of out-of-school punishments were for nonviolent offenses, such as disrupting class.

The new policy would forbid school districts from adopting a "zero-tolerance" approach to discipline, or automatic punishments for certain offenses.