BOSTON -- A local high school was locked down Monday after a shotgun shell was found on the lobby.

Students at Milton High School were kept in their classrooms from approximately 1 p.m. until they were dismissed later than usual at 3 p.m.

During that time, police searched the school with five bomb-sniffing dogs -- a search that they said is standard protocol any time ammunition or weapons are found.

Nothing else was found on the high school's campus. Police said students or staff were never in any danger.

"The school department and students did a great job," said Milton Police Lt. Kevin Foley.

Ironically, police told NewsCenter 5 that just last week the school performed a "lockdown drill."

It is not yet known where the shotgun shell came from.