The boy apparently fell asleep Monday morning and wasn't discovered until nearly 2 p.m. The substitute bus driver was placed on administrative leave.
"All of us who have kids can put ourselves in that boat," Chris Hall, assistant superintendent for support services, said Tuesday afternoon. "I feel for this family, and we're very apologetic to this family going forward."
Hall said the boy, a San Lauren Elementary School student, was in good shape and good spirits when he was found.
The boy's mother was notified, and he was sent home.