A mum planted a recorder on her son with autism. Then she heard the mockery from teachers.

A mum in the US has uncovered extremely concerning alleged behaviour after sending her autistic son to school carrying a hidden sound recorder.

Two staff members from the Hope Academy in Louisiana have been fired since the recordings were taken public, WBRZ reports, as on the tape both teachers and students can be allegedly heard bullying the 12-year-old.

Mum Milissa Davis decided to take action with the tape recorder when she noticed changes in her son Camden’s behaviour.

“He started wetting the bed again and had increased anxiety,” she posted to Facebook recently.

“The separation anxiety became increasingly worse. I was suspicious of something going on at school so I decided to send a recorder in his book sack.”

She said she enrolled Camden in the school last year “in hopes of him receiving specialised education so he can learn in a specialised environment”.

What she heard on the recording was "unbelievable", Milissa says.

"Not only was Camden being bullied by peers but he was being bullied and threatened by his [teacher's aide] and teacher.

"When Camden tries to ask for help from another teacher he’s told to get away from her and that she’s reporting his negative behavior to Santa.

"Camden used to be a free-spirited, fun-loving child and now he struggles with trust and separation anxiety."

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A teacher can be heard in the recording saying to Camden, "You’re just writing the word. What is hard about it?", WBRZ reports.

When the 12-year-old grunts in response, the teacher mimics him in a mocking fashion before later adding, "Camden, why don’t you have anything written down? That’s why you can’t sit with everyone. Tell your mumma that".

A private conversation between the teachers is also overheard, with one allegedly saying to the other:

"Let’s see what they do with him in f***ing public school. He was going to go to Live Oak Middle. He wouldn’t make it for a minute."

According to the school, Milissa did not bring the recording to their attention before posting it to social media.

"The parent has also refused to meet with Hope Academy to discuss the actions we have taken to address the issue," the school's statement read.

But Milissa says she has "hours of recordings" and now has severe trust issues herself when it comes to educators and entrusting her little boy to the school system.