Current funding problems will pale into insignificance when schools are faced with the cost of paying support staff for the extra work and responsibility envisaged in the new workload agreement.
Costs could rise by up to 40 per cent as local authorities agree new grading structures. Heads who believe that employment powers given to schools in the 1988 education reforms allow them to set their own pay rates for non-teaching staff may be in for an unpleasant surprise.
Support staff are very badly paid, with hourly rates as low as pound;4.96.
Four in 10 schools do not pay teaching assistants during school holidays and many assistants work extra hours for no additional pay.
"Teachers often forget that our members are paid for a set number of hours," said Christina McAnea, national secretary for education for the public-sector union Unison.
Unison represents thousands of school staff, from caretakers to classroom assistants. It signed January's workload agreement, along with the GMB, the other union representing support staff. Both unions remain committed to the deal.
"We were keen to be involved," said Ms McAnea. "We saw what happened in Scotland, where we had no involvement." The McCrone settlement was designed to give Scottish teachers a 35-hour week, but it did not address the pay and conditions of support staff, who were supposed to take up some of the teachers' burden.
January's agreement fills that gap, with a commitment to "new career paths", alongside a pay structure that "reflects training, skills and responsibilities". Ms McAnea sees the deal as a way to lever in higher pay and improved conditions of service for her members.
Unison is in national negotiations with employers. But as support staff pay is set at local level the union is also pressing for deals with individual councils. Where employers are reluctant to co-operate it has taken court action.
In Lancashire, the union launched an equal pay claim on behalf of nearly 1,000 teaching assistants - the largest action of its kind in the UK. "We are 100 per cent confident that we will win the case if it comes to court," said Ms McAnea. But that now looks less likely as Lancashire has returned to the negotiating table.
"Court action isn't the ideal solution," said Ms McAnea. "But it did send a message to other employers that 'if you don't negotiate with us you'll be next'."
In Nottinghamshire, the problems were different. Unison believed it had an agreement, negotiated with the authority - but schools refused to implement it.
The deal, signed in September 2001, agreed a three-level structure for classroom assistants. The top grade gave qualified staff up to pound;18,400 a year. But one in six Nottinghamshire schools refused to implement the changes, forcing Unison officials into school-by-school negotiations.
Eighteen months later, two Nottinghamshire schools - Joseph Whitaker comprehensive and Samuel Barlow primary - have still not implemented the agreement.
"Unison reps told me that I had no choice," said John Loughton, headteacher of Joseph Whitaker. "But there are matters of principle involved."
Nottinghamshire's view is that "schools have the responsibility for managing their staff". But both the county and the union are taking legal advice.They could save some money by examining a London employment appeals tribunal's landmark ruling on a constructive dismissal claim by Kent deputy head Diane Green.
The tribunal ruled in March that a school governing body could only be treated as the sole employer if it exercised the employment powers laid down in the 1988 Education Reform Act - appointment, discipline, suspension or dismissal.
Otherwise the employer is the local authority. This means that maintained schools will have to implement any locally agreed deal and local authorities will have to monitor schools to ensure compliance.
Any feet dragging on the issue will be raised by Unison representatives at meetings of the monitoring group set up to keep an eye on the reform process.
"We have made it clear all along that our support and continued endorsement for the workload agreement is all concerned with what happens at local level," said Ms McAnea.