A West Auckland school principal is facing a revolt by a group of parents who are concerned about bullying, high staff turnover, unhealthy toilets and treating parent volunteers "like a slave".

The parents at Henderson Valley School have written an open letter asking the board of trustees to either set up a "mentor/supervision process" for principal Janet Moyle "or take steps to seek a suitable replacement".

The letter has been signed by the parents or caregivers of 37 children, a tenth of the school's roll of 363.

Moyle referred Herald enquiries to board chairman Michael Alofa, who has called an urgent board meeting to discuss the letter tomorrow.

"Henderson Valley School takes very seriously all concerns raised with it and is committed to handling these in line with best practice," he said.

"It is important to note that our students are our absolute priority, particularly their education and their health, safety and wellbeing.

"We can confirm that our school is liaising with NZ School Trustees Association and the Ministry of Education to ensure that we act in line with MOE/NZSTA expectations."

The open letter says parents have observed "a serious decline in the offering of the school and a growing lack of trust and confidence in the school management" since Moyle was appointed principal two years ago.

"We have observed a massive turnover of staff and a noticeable decline in the school roll," it says.

The roll has fallen steadily since before Moyle arrived, from 392 in July 2015 to 387 in 2016 and 370 in July last year, and was 363 in September this year.

A parent, who declined to be named, told the Herald the parents' main concern was bullying.

The school's bullying policy states: "Henderson Valley School takes a zero-tolerance approach to bullying."

But the open letter says: "There are a number of parents very concerned with what appears to be a steady increase in bullying culture at HVS.

"Many parents have reported that they have discussed this issue with the principal only to be told she is 'not aware of any bullying incidents'. We question how more than one parent could be given this response?"

The letter says staff are also unhappy.

"Why have so many great teachers left HVS over the past two years?" it asks.

"Why are so many teachers commenting to parents about the unpleasant or difficult work environment they find themselves in and reporting issues of micromanagement, pressure to 'comply' and the failure of management to listen to teachers' views on proposed changes?"

Parents who volunteer their time to coach sports teams and raise money for the school say they do not feel valued.

"Why are sports volunteers treated so poorly?" the letter asks.

"Some parents describe how they felt they were treated 'like a slave' and it was expected they are involved year on year.

"Why have all of the former Fundraising Team members withdrawn their services to the school? How does an entire team become so despondent?"

The parent who spoke to the Herald said Moyle wanted to replace the fundraising team with a parent-teacher association.

The letter says many bathrooms in the school "are old, smell awful and [are] unhealthy".

"The toilets in the hall and in the pool shed are foul and need replacing," it says.

"The toilets and handwashing facilities are unsanitary and could be considered a risk to children's health. Some parents have reported they have supplied and/or offered to supply the school with soap for the toilets and have been refused.

"The boiler operation process and maintenance needs to be reviewed, as the classrooms have been very cold and there is a lack of heating during winter."

Parents also say in the letter that school sports are "seriously lacking", competition "has been taken out of the school athletics day", there has been a noticeable reduction in school trips, and a camp for Years 3 and 4 children was moved onto the school field without adequate consultation with parents.

"As a group, we have acute concerns about the principal's ability to successfully manage and operate our school," the letter concludes.

"We request for the Board of Trustees to review the principal's ability to perform her duties to an appropriate standard, with particular focus on the concerns identified within this letter.

"If deemed appropriate, the Board of Trustees should seek guidance on a suitable mentor/supervision process for the principal or take steps to seek a suitable replacement."

Ministry of Education deputy secretary Katrina Casey said the ministry was aware of the open letter.

"To date, we have not been contacted by any parents," she said. "We are here to provide support and guidance, if needed at any time."