Police have been called into Glen Eden Intermediate School after a student's mother allegedly assaulted a 13-year-old boy.

Principal Maree Stavert said the woman came on to the school grounds at lunchtime on Monday and physically assaulted the boy, who was not her son, in the playground.

She said social media reports that the boy was taken to hospital were not correct and the boy was back at school today.

"He was a bit sore but he was not badly hurt," she said.

"It's not what you expect to happen. But it's just something have to work through with. I haven't seen anything like it."

Stavert said she could not comment on the reasons why the woman allegedly assaulted the boy because police were investigating.

"The boy is not at fault. It's all under police investigation," she said.

"Once the police have confirmed who it is, she will be trespassed."

The school has come under fire on the Glen Eden Community Facebook page for not making a statement about the incident.

"Don't know why the school haven't released a statement to parents given the seriousness of the situation and the fact that people's children will of course be commenting on it at home," one parent said.

But another said: "I can understand why the school hasn't released a statement. To protect the children involved. I'm sure the adult will be dealt with by police it's a heartbreaking situation."

A police spokeswoman said police are investigating the incident.

"Police are working to establish the full circumstances surrounding this incident, and as those inquiries are ongoing, Police are not in a position to comment further at this stage," she said.

In 2018 a mother at Mt Albert Grammar School was charged with assaulting a 17-year-old student who had allegedly been bullying her daughter.

The judge ruled that she made a "bad decision" which should not impact on the rest of her life, and discharged her without conviction.