Weston High School was placed on lockdown and then evacuated as a precaution because of a threat.
The lockdown began at 12:30 p.m. on Wednesday, after a teacher found a note with a threat to kill a teacher and 25 students, according to a police source with knowledge of the investigation.
A police officer who was at the school on an unrelated matter was told about the note.
The building was then evacuated and students were moved to other schools as a safety measure, according to school officials.
The note has been sent to the state crime lab for further testing, the source said.
Anyone with information is asked to call police.