WASHINGTON — African-American or Hispanic students may be more likely to be suspended, expelled – or even arrested – than their white peers. What’s not clear is why.

Is it discrimination, as some civil rights groups contend, or are minority students committing more infractions? Or are minority students receiving tougher punishments than whites for similar incidents?

What is known, from an Education Department civil rights report released Tuesday is that Hispanic and African-American students comprise nearly three-quarters of students involved in school-related arrests or cases handed over to police.

The report also found that black students are more than three times as likely as white pupils to be suspended or expelled. Also, a disproportionate number of black students with disabilities are strapped down or subjected to other restraints.

“The sad fact is that minority students across America face much harsher discipline than non-minorities, even within the same school,” said Education Secretary Arne Duncan.

Neither Duncan nor the report provided the details behind the numbers.

Civil rights activists said they weren’t surprised by the results. They blamed get-tough, “zero tolerance” policies that they say contribute to a “schools-to-prisons” pipeline. The problem, they say, is that zero tolerance applies more to minorities than white children. They say it’s time for a dialogue on appropriate and fair discipline.

Duncan said some school officials might not have been aware of inconsistencies in how they handle discipline, and he, too, hoped the report would be an eye-opener. “We’re not alleging overt discrimination in some or all of these cases,” he said.

Judith Browne Dianis, co-director of the Advancement Project, a think tank that specializes in social issues affecting minority communities, said research shows that black and Hispanic children are punished more harshly for the same offenses than white children.

Some think it’s necessary to crack down on minority kids for small infractions. “There’s bias in classrooms. There’s also this perception of children of color as being criminals,” she said.

Raul Gonzalez, legislative director at the National Council of La Raza who taught school in New York, said zero-tolerance policies in both schools and courtrooms have created a system that takes children out of school and ultimately leads them into prison, where they become hardened criminals.

He said more moderate responses are needed in schools, and he hopes the report will lead to a change not just to school policies, but also to state laws.

“We’ve lost control of all judgment here, and it’s almost always a black kid or a Hispanic kid” affected, Gonzalez said.