Independent advisers say that calls from state schools asking for help have risen five-fold as heads struggle to balance their books. They are advising schools to "think big" by fostering closer links with businesses and well-off former pupils.
Mark Jefferies, managing director of the Hertfordshire-based fund-raising consultancy, Craigmyle, said relying on parent-teacher associations was rarely cost-effective.
Events such as dinner dances should not be arranged more than twice a year because they put too much pressure on people to attend and created "donor fatigue".
They also cost money to put on, in terms of hiring bands or discos.
"These are good as social occasions and they should not be sniffed at because they get people involved in helping the school and it makes them feel they are doing their bit.
"However, they cannot be relied upon for raising large amounts," Mr Jefferies said.
"Although it is rare, schools can raise up to pound;1m over time if they do things right."
Parents can be asked to covenant set amounts of money per week or term, over a specified period of time. For every pound;100 donated by a family over a year, the school can claim a further pound;28 from the taxman.
Parents who give an undertaking to donate money allow schools to plan ahead and use the pledges against borrowing.
Alternatively, parents can donate using "gift aid", which is similar to a covenant but holds no promise of contributions over time. The school can also claim back the tax.
But "cold-calling" past pupils and local firms for money often proves fruitless. "Former pupils who suddenly get letters from their schools asking for money 20 years after they left will probably just throw them in the bin.
"However, if schools start setting up a data-base of alumni and keep in touch with them once a year, for example, by publishing a newsletter of what is happening at the school, they are far more likely to get positive responses.
"Similarly, it is worthwhile fostering links with local businesses by getting them involved in projects at the school, or in mentoring."
Mr Jefferies said schools helped so far had generally raised between pound;100,000 and pound;600,000 over time.