Teachers and pupils had to be barricaded in their classrooms following a raid on a security van in West Sussex.
Firearms officers were deployed to search the grounds of The Vale First and Middle School in Findon Valley last week.
The school was placed on "immediate lockdown" with no pupil or member of staff allowed to leave classrooms while officers scoured the site.
Earlier, the crew of a Group 4 Securicor van at a Tesco store in Chichester had #163;17,000 stolen from them after being held up at gunpoint.
Officers entered the school in search of suspects and arrested one as he was walking out of the front gate, and the other in the school grounds.
Dominic Mendy, 30, and Danny Palmer, 31, were later arrested and remanded in custody, Sussex Police said.
In a letter to parents, headteacher Tony Lovatt said no child was harmed and no weapons were brought into the school.
"The staff reacted promptly and the police have praised the school for their quick thinking and the security measures that are in place," he said. DM.