A school principal is apologizing for a lesson that used the Underground Railroad as the basis for gym class activities.

David Stewart is principal of Madison's Trust Elementary in Ashburn. He wrote a letter to parents calling the lesson "culturally insensitive to our students and families."

Loudoun County Public Schools spokesman Wayde Byard said the gym class began with a lesson about the Underground Railroad as part of Black History Month. Students in grades 3-5 were then split into groups and challenged to overcome a physical obstacle.

Byard said the school system received about 10 complaints from families.