A Whanganui school that allows a relief teacher to have her baby in the classroom while she teaches has angered some parents who say their children's learning is being neglected.

Kaitoke School has a relief teacher take over for two hours a day in a class for students around six years old. But as part of the deal she's allowed to manage the class with her baby, believed to be aged about one, present.

One boy at Kaitoke School first alerted his mother to the baby a couple of months into the relief teacher's stint at the school this year. Her son was frustrated and she said his reading level had also dropped.

"I just don't understand why the child cannot be put into some sort of daycare while she's teaching," the mother said.

"She's paid to teach this class for those two hours and you can't give your 100 per cent focus on those children if you've got your own child that you've got to worry about."

She said they were told in a Facebook post about the relief teacher but that it didn't make it clear her baby would be in the class with her.

The parent, who chose not to be named so her son would not be identified, was frustrated by the school's response to her concerns.

"I went to the principal because I wasn't happy and I was pretty much fobbed off by her.

"So then I went and wrote a letter to the Board of Trustees and they took their time to get back to me and then told me that this is what it is, the baby's staying, it's written into her contract."

The parent has now enrolled her son at another school.

She said she had found 11 parents of the 19 kids in the class that also said it wasn't right for the school to allow the teacher to have her baby in the classroom. A newsletter was even sent out to parents when the school got word of a potential petition from parents.

"Saying that they don't condone this [the petition]," the parent said of the newsletter.

"They're not even interested in what we have to say and they won't even look at it.

"It's kind of like ... the baby stays and it doesn't matter whether the baby affects your child's education or not."

Kaitoke School's acting chairman of the Board of Trustees, Rob Crawley, said the baby was in a carry pack and slept for the majority of that time.

He said the school had received two complaints and that they had been addressed appropriately.

Crawley also said the school had received a number of letters of support from parents who liked that the school had a holistic view to teaching.