KINGSPORT, Tenn. -

For many people, September 11 seemed just like yesterday. But for some, it’s a lesson from history books.

A history teacher at Sullivan South High School, who focused on the attacks in class on Tuesday said most of his students were in preschool or kindergarten in 2001; they grew up knowing little about Bin Laden and terror threats.

"I remember the changes that happened after September 11th. These kids don't. Their world is post-September 11,” said Ben Davenport, history teacher. "They don't understand what it was like beforehand, to see why airport security is the way it is."