A fifth-grade teacher in Massachusetts who held a “mock slave auction” and used a racial slur in a classroom has been placed on paid administrative leave, the district superintendent said.

The teacher, who has not been publicly identified, held the mock auction in January during a history lesson on the economy of Southern colonies, the superintendent of Public Schools of Northborough and Southborough, Gregory L. Martineau, said in a letter to parents dated May 29.

During the lesson, the…