The police in Northern Virginia are investigating a report by a black 12-year-old girl that three white boys in her grade held her down, covered her mouth and cut off lengths of her dreadlocks on a playground at their private Christian school.

The girl, Amari Allen, who is in sixth grade, and her family said the assault happened on Monday during recess on the playground of the school, Immanuel Christian School in Springfield.

They said the three boys, whom they would not name, had been bullying Amari since the start of the school year in August.

“They put me on the ground,” Amari said on Friday in a phone interview. “One of them put my hands behind my back. One put his hands over my mouth. One cut my hair. They were saying that my hair was ugly, that it was nappy.”