Most independent schools require a full term's notice to withdraw a student without penalty, and that means to start a new school in 2017, parents have just weeks left to avoid incurring an extra term's fees.

Some parents have learned this the hard way.

Mosman parent Mark Rosenberg gave Kambala in Rose Bay notice three weeks into term 4 last year that his daughter would be leaving after eight years at the school, or more than three months' notice. He says he did so as soon as the new school confirmed her place.

But now he is in a stand-off with the independent girls' school, which charges fees of $30,189 a year for years 7 to 10. The school says he owes $8700 for term 1, 2016 fees in lieu of giving sufficient notice.

Dr Rosenberg is refusing to pay, calling the school's actions "double dipping" as it was able to fill his daughter's place and so was evidently not left out of pocket by her departure. Kambala has engaged a debt collector to chase the unpaid fees.

"Legally they may have a right, but morally and ethically it's a pretty poor show considering they've already filled the place and considering they actually say to you the reason they do it is so they are not caught short – and they haven't been caught short," he said.

"They are double-dipping. ...They really don't care whether you've been there for 10 years or not."

Kambala principal Debra Kelliher said the school, a not-for-profit organisation, "has a very clear and transparent policy regarding fees. The school plans for, and commits to, a range of staffing costs and services in advance. It is not fair that the withdrawal of a student in shorter than the agreed notice period should become a cost incurred by other parents."

She said the school would exercise discretion over fees in "exceptional cases of personal hardship or family bereavement," but said, "there were absolutely no exceptional circumstances in this particular case."

Chief executive of the Association of Independent Schools of NSW Geoff Newcombe, said it was standard practice for schools to require a term's notice.

"Where a student is withdrawn without sufficient notice, the school may not be able to fill that place at late notice which results in a loss of income for the school," Dr Newcombe said.

In the public school system, there is no notice period required for enrolling or withdrawing students.

Natalie Mactier from private school enrolment service School Places says there are 11,000 available places nationally on their books, the majority of which are for "last minute" places to start in 2017 or 2018.

"We find that we get a scramble of parents at this time of year, those ones that are wanting to make a change, they know that they need to lock something in and give notice by the end of school holidays."

Year 7 places are usually offered in April of the previous year, but many families are looking to change at other stages.

"Year 7 is a very popular year for parents to move between the public and the private system so you do find that year 7 is particularly hard to get into. But that doesn't mean that year 5 or year 9 there aren't vacancies," she said.

Ms Mactier said that more than the long notice periods, unrefundable waitlist fees (usually of $100-$250) and enrolment fees of up to $1000 tended to be at the top of parents' lists of complaints about dealing with private schools, particularly since they often can't get information about how high they sit on the waiting list and therefore how realistic are their chances of getting in.