South Windsor High School was dismissed early Thursday.
Police said they found a note with a vague threat about a bomb at the school. The school was evacuated so investigators could look into the threat.
No evidence has been found that indicates there's an actual bomb or that the students are in danger, but school officials decided to close the campus as a precaution.
All seniors and juniors who drive to school were allowed to go to their cars and go home.
Freshmen were brought to Wapping Elementary School and sophomores were brought to the South Windsor High School Auditorium.
Buses were slated to pick up students at the regular time, but parents could pick up their students.