A bomb threat forced the evacuation of Sandy Hook Elementary earlier today, the sixth anniversary of the Newtown school shooting.

Newtown's school superintendent says someone called the main office saying there was a bomb in the building.

Students were evacuated to a nearby senior center, where buses started taking them home around 11 a.m. 

Chaperones stayed with each child until they were reunited with parents or guardians.

Police and the National Guard did a sweep, and police cleared the scene around noon. Investigators remain tight-lipped about the specifics of the threat or where it might have come from.

Jack Rodriguez's dad received a text saying something was wrong at the school.

"It's no good for the fathers, for the mothers, for the babies,” said Lester Rodriguez. “For everything, this is too hard for this family, for today."

Frank Shane and his therapy dog Chance work with the families of Sandy Hook victims. He says even a threat can traumatize kids.

"Very emotional because it brings it back.  It doesn't become an anniversary then; it becomes the day again," says Shane.

Sandy Hook Elementary has received several threats before – mostly from conspiracy theorists who believe the shootings here were a hoax. This is the first time a threat has come in on the anniversary.

Other schools in Newtown remained open today but were put under a shelter-in-place order to limit visitors.