Four out of 10 secondary schools and almost a third of primary headteachers are happy with their budgets, a survey reveals.
It shows a sharp rise in the number of heads in England who say they have enough money to run their schools.
But the research by the British Educational Suppliers Association also reveals widespread concern about long-term funding, with 60 per cent of headteachers fearing that it will get worse over the next five years.
John Dunford, general secretary of the Secondary Heads Association, said:
"Most teachers recognise that more money has been made available, but we look nervously to the future.
"There is never enough money in a budget to do all the things you want to - and there are often questions asked about how it is allocated."
The study, based on responses from more than 1,000 schools last year, found that 30 per cent of primary and 40 per cent of secondary heads were happy with their school budgets.
The figures show a sharp rise since BESA's survey in 2003, which found that just 17 per cent of primary and 12 per cent of secondary schools were content.
David Hart, general secretary of the National Association of Head Teachers, said: "Although the figures have risen, they are still very low and not satisfactory enough.
"The issue is not just funding this year or next year - it is about sustainability for future years."
The survey reveals that primary heads are spending less on classroom resources, with the average school spending pound;28,040, a fall of 1.5 per cent.
In secondaries more cash is being spent on books and classroom aids, with the average school spending pound;139,545, a rise of 0.6 per cent.
Researchers also found that 69 per cent of primary and 65 per cent of secondary heads said resources were a lower priority than recruiting and rewarding teachers.
More headteachers are also employing bursars and school managers in a bid to juggle and stretch their finances.