P&Cs are asking parents for annual voluntary contributions of $200 per child or more to help pay for education programs as well as iPads, upgrades to toilets and additional support teachers.

This is on top of voluntary school fees, which NSW Department of Education figures show significantly boost schools' coffers.

The latest published figures show some public schools, such as Baulkham Hills High, raise as much as $250,000 a year through fees which are designed to "enhance educational programs". But many schools also rely on P&C donations.

At Epping Boys High, parents are asked to contribute to three P&C funds, including grounds maintenance and building funds, totalling $400. That is in addition to the voluntary school fees, which exceed $400.

Last year, the P&C bought the school a 25-seater bus with the voluntary contributions but has also used the parents' donations to buy language textbooks, workbooks and to pay for student welfare support.

Willoughby Public's P&C contribution is $200 per child while at Neutral Bay Public, the annual P&C contribution last year was $180 for one child, rising to $450 for three or more children. Neutral Bay's P&C's fundraising target was $200,000.

But principals warn that it is often only parents in wealthy areas who can afford the voluntary levies, creating a bigger divide between rich and poor schools.

Geoff Scott, the president of the NSW Primary Principals' Association, said P&Cs were often asked to support programs such as gifted and talent classes, art workshops or school bands.

"There are some wealthy P&Cs because parents have high-disposable incomes and they can fund programs supplementary to the school plan but there are many schools where parents are not high earners," Mr Scott said.

"There is a fundamental inequity that Gonski (the needs-based funding model) would address if it was fully funded, because irrespective of your postcode, Gonski would ensure no child missed out."

The Turnbull government has said it would not fund the final two years of the Gonski school funding deals and would seek to strike new funding arrangements with the states from 2018 – the year two-thirds of the $10 billion funding was to start flowing.

The president of the NSW Federation of P&C Associations, Jason Vials, said schools that struggled to raise large amounts were often the ones that needed it the most in rural and remote areas or with a large population of non-English speakers.

"There is no doubt that P&Cs are being asked to contribute significant amounts to schools and this has been going for some time because of chronic under-funding," Mr Vials said.

"Parents are asked to even contribute boxes of tissues because school cannot afford them, as well bring-your-own-devices because schools don't have the money to buy things like laptops and iPads."

A NSW Department of Education spokesman said programs such as Reading Recovery, was a department-funded program but others could be funded by P&Cs.

"Using department-provided global funding and the Resource Allocation Model (RAM), principals develop gifted and talented programs in consultation with their local school community," the spokesman said.

"Individual school P&C groups may choose to supplement existing programs."