Hamden High School was evacuated as a precaution after someone called school administration and said there was a bomb in the building and it was "going to go off," police said.
Police were called at 11:41 a.m. on Wednesday, students were moved from the school to bleachers by the football field, then to the Hamden Ice Rink.
The bomb squad responded, swept the building and determined that the scene was clear.
Police did not allow parents in to pick up their children, but some said they understood.
Students were allowed back into the building as of 1:45 p.m.
