An Ohio teacher who told a black eighth grader that his friends would “lynch” him if he didn’t finish his work has been put on leave, the school district said, calling the student a “hero” for standing up to her.

The 13-year-old student, Nathan Bell, was chatting with his friends at Mason Middle School in Mason, Ohio, about 25 miles north of Cincinnati, on Dec. 4 when his social studies teacher became frustrated, his mother, Tanisha Agee-Bell, said in a phone interview on Sunday.

The teacher told Nathan, who was the only black student in the class, that “if he didn’t get back on task, then his friends were going to form an angry mob and lynch him,” Ms. Agee-Bell said. Nathan responded that her comment was racist, and the teacher, Renee Thole, “kept asking him why,” Ms. Agee-Bell said.

“Her job is to teach American history to eighth graders,” Ms. Agee-Bell said. “How can you teach American history and you don’t understand the impact of your words to your students, given our nation’s history?”