School officials had announced late Wednesday morning that the school in King of Prussia was being locked down, but that students were not in danger.
Police tell Action News that there was some type of fight Wednesday morning in the school cafeteria.
Following the fight, as students were leaving they threatened to come back and seek revenge and further violence.
As a precaution, school officials locked down the high school and requested a heavier police presence.
No arrests have been made and no injuries sustained in the altercation.