A man in his sixties, thought to be the caretaker, sustained bruising after being assaulted outside Baylis Court School, in Gloucester Avenue, Slough, as children were leaving for the day.
Four boys, aged between 15 and 16, have since been arrested on suspicion of assault occasioning actual bodily harm after the incident on Thursday, March 8.
Police are now investigating the incident.
A parent, who did not want to be named, told The Observer: "I just saw my girls running out of school after they saw the trouble outside the gates.
"It was scary - the police came quite quickly but I'm really, really disgusted. It is a very good school but an incident like this just spoils everything. The children were scared by it all."
The school sent a letter to parents following the incident however headteacher, Maureen Ball, refused to comment when The Observer tried to contact her.
A student at the school sixth form, who wanted to remain anonymous, added: "I was walking to pick up my sister from the school and a group of boys rushed past me.
"One of the teachers told me to stop and go back but I carried on walking.
"I realised things were out of hand though and stopped because I was so shook up. Parents were walking past to pick up their kids from nearby schools - it's a worrying thing.
"It's a very respectful area and something like this has never happened before at Baylis - it's like a home to me."
Arina Hester, headteacher at nearby Godolphin Infant School, in Warrington Avenue, said: "We are aware of the police involvement in the incident but it had no impact here.
"We were reassured the appropriate police action was taken. We have had no concerns raised from our parents."
The boys have been released on police bail until April 10, pending further inquiries.