Giving secondary schools more money makes only a small difference to overall GCSE results and has no effect on GCSE achievements in English, Government-commissioned research shows.
The study also found that although lower pupil-teacher ratios led to slightly better overall GCSE results there was no evidence of them having any impact on English or maths results.
Last month Gordon Brown, the Chancellor, made great play of an open-ended commitment to raise per pupil funding from pound;5,000 to the pound;8,000 a year currently spent in the independent sector in a bid to cut class sizes.
The London university Institute of Education research suggests that even if the Chancellor did reach his goal it would only have a limited impact on GCSE results.
It also found no evidence that improving the ratio of pupils to non-teachers in a classroom led to better GCSE results.
But John Dunford, Association of School and College Leaders general secretary, said policies such as the specialist schools programme proved extra funding did make a difference. The research used government data to calculate the progress of 450,000 pupils in English schools between their national tests as 11-year-olds in 1998 and GCSEs in 2003.
Researchers used school budget returns to calculate spending per pupil in approximately 3,000 secondaries. A formula was used to eliminate factors, such as the number of pupils with special educational needs or on free school meals, which lead to higher school funding levels but are also likely to influence GCSE results.
The report estimates that an annual extra pound;100 per pupil over five years would mean an average improvement of about 0.3 in a pupil's overall GCSE points score.
In science the same funding rise was calculated to lead to an extra 0.05 of a grade on a science GCSE. In maths GCSE results improved only for the 40 per cent of the pupils with lowest attainment at the age of 11. There was no evidence of any impact on English.
The research found that spending an extra pound;100 per pupil per year to cut class sizes would have between two to four times more of an impact on GCSE results than a general funding increase.
But it would still be limited. One less pupil per teacher in a class would mean an average improvement of no more than 1.2 in a pupil's overall GCSE points score. It would mean an increase of up to 0.25 of a grade in science but nothing in English and maths.
Steve Sinnott, National Union of Teachers general secretary, said: "It is unrealistic to expect a massive improvement from a tiny change." This weekend his members are expected to vote for a campaign to cut class sizes.
A Department for Education and Skills spokesman said investment together with reform was raising standards. But Anna Vignoles, one of the researchers, said: "If you want to improve standards in secondary schools, spending more might make an impact but there are probably better ways."
Measured success? Researchers found no evidence that having more teaching assistants per pupil led to better GCSE results