The idea that state education in England should be free of charge is enshrined in law. But parents face a growing array of hidden costs.
In some cases schools are even breaking the law to charge parents for activities such as singing lessons that should, by law, be free.
The Government also hopes to introduce legislation this year that will allow local authorities to charge parents for their children's bus journeys to school.
David Hart, general secretary of the National Association of Head Teachers, warned of a "creeping privatisation" of education. "It is understandable because local authorities are strapped for cash," he said. "I know parents find it irksome but they should put the blame where it really lies, with those who are responsible for school funding."
Mr Hart said he was far more concerned by cases where parents were being asked to pay for school essentials than when they were unhappy with the costs of uniforms, trips and other activities.
John Dunford, general secretary of the Secondary Heads Association, said the bus charges and other developments brought into question the whole idea of free state education. "There is a pattern developing and I have found it increasingly worrying," he said.
Here are some of the key areas where schools are charging parents or asking for contributions:
Most local authorities charge schools for peripatetic singing tuition, despite legislation stating that it should be provided free to pupils.
Under the 1988 Education Reform Act, vocal tuition is singled out as distinct from musical-instrument lessons, for which schools are entitled to charge. The Act states: "Individual or group vocal tuition which is provided within school hours must be free."
But a TES survey of 50 local authorities last month revealed the majority charge between pound;7 and pound;28 an hour for the services of a peripatetic singing teacher. Others charge as much as pound;84 per term for weekly lessons of 20 minutes. Tuition is generally offered in groups of up to four pupils. One-to-one lessons incur an extra cost.
Some authorities, such as Bury and Devon, send the bill for tuition directly to parents. But most bill schools, leaving it up to each individual institution whether, and to what extent, they pass on the cost to parents.
Russell Parry, of Leicester city council, which charges pound;25.20 per hour, said: "We know it's illegal to charge parents for singing tuition given during the school day, so we don't do that. We leave it up to the schools whether they charge parents."
Only a handful of authorities, such as Walsall and Redcar and Cleveland, make no charge at all, claiming that legislation prevents them from doing so.
Colin Brackley Jones, chief executive of the Federation of Music Services, said: "The law no longer matches what is needed, so it requires revision.
It makes a nonsense of current practice. There is no rhyme nor reason for viewing the voice differently to other instruments."
The pressure on schools to introduce uniforms has grown steadily over the past year with both Charles Clarke, Education Secretary, and David Bell, the chief inspector, praising the impact they can have on standards.
Department for Education and Skills guidance to schools states that governing bodies must consider carefully the cost of a school uniform before introducing it; "No school uniform should be so expensive as to leave pupils or their families feeling socially excluded".
However, parents continue to complain that uniforms are too expensive.
The average secondary uniform costs around pound;160, and parents have reported cases where state schools have demanded they buy blazers costing more than pound;45.
Local authorities have traditionally helped towards the cost of uniforms for poorer parents. However, there is no statutory requirement for them to give this support and the proportion providing it has now dropped below two-thirds and continues to fall.
One of the latest authorites to abandon this assistance is Essex, which stopped providing it on Wednesday. A spokesman for Essex County Council said the authority had been "very reluctant" to make the cut but had no choice after receiving a disappointing funding settlement.
Free transport is at present available for pupils who attend the nearest suitable school, providing it is more than two miles away if they are under the age of eight and three miles away for those aged eight and above.
But this is set to change under the School Transport Bill, which will be debated in Parliament this year.
Local authorities will be able to charge families for using school buses, except if their children are eligible for free school meals.
The scheme will be piloted for three years in up to 20 local authorities and expanded nationally if it proves successful.
Teaching unions have warned that the scheme may back-fire and result in more parents opting to take children to school by car.
The DfES insists the charges will only be small and that it will look carefully at the experience of the pilot authorities before expanding it.
Schools are not allowed to charge for transport or activities which take place during school hours. The DfES says that schools may, however, ask parents for voluntary contributions.
"The contribution must be genuinely voluntary, though, and the pupils of the parents who are unable or unwilling to contribute may not be discriminated against," it says.
However, some parents who have told schools they cannot afford a trip claim they have then faced "emotional blackmail". Teachers will often tell parents that an outing must be cancelled for the whole class if their child cannot pay to attend. The DfES guidance encourages teachers to make this decision. It states: "Where there are not enough voluntary contributions to make the activity possible, and there is no way to make up the shortfall, then it must be cancelled."
Parents who receive benefits can recover the cost of residential trips which take place partly during school hours as well as out-of school trips which are a necessary part of the syllabus.
Soaring numbers of secondary schools are bidding for specialist status, and 90 per cent are expected to gain it within the next three years.
The status is highly attractive as it brings schools into a network of high-performing secondaries and - most importantly, for some - provides them with a one-off pound;100,000 capital grant from the Government plus annual top-up grants of pound;126 per pupil.
To gain the status schools must raise pound;50,000 in sponsorship, of which a minimum of pound;15,000 must come from a business.
A Specialist Schools Trust spokesman said that figures were not available to show how most schools had raised their money.
But he said that parental contributions were very significant and "varied wildly".
"It can range from very small amounts to the maximum we allow, which is pound;35,000," he said.
A constant refrain from heads during last year's funding crisis was that their parent teacher associations had been raising money for essentials, rather than extras.
Parents also face demands from some schools to sign covenants, such as the one proposed by the London Oratory school in 1999, where parents agreed to pay up to pound;35 a month to help it out of funding difficulties.
Heads report that certain subjects, particularly music and sport, are taught for less time than in the days before the national curriculum. This means that pupils who enjoy them find themselves spending more time attending after-school clubs, which can charge.