While independent schools with boarding facilities might be able to plug any funding gaps by recruiting overseas, those relying on UK-based pupils are being advised to market themselves better.
Dick Davison, of MTM Consulting, which advises private schools, said there were up to a million families who could afford school fees but had not been persuaded to pay them.
"Schools have to be more savvy. I think they could be doing better," he said. "There are families who could broadly afford fee-paying schools but aren't hearing the arguments presented well enough."
Schools should also look at their pricing structures and avoid excessive fees hikes, he said.
"Schools are asking us if their strategy for the next five years is sound. They're getting their ducks in a row now because they know the recession is coming," he said.
Bernard Trafford, former chair of the Headmasters' and Headmistresses' Conference and head of the Royal Grammar School, Newcastle, which charges nearly Pounds 9,000 a year, said: "We're starting to hear a few problems and we're all braced for a flurry of that. We're being very watchful at the moment."
One common hardship being faced by parents is an inability to find the cash for school fees by releasing equity from their homes.