Government claims that extra money for England's schools has boosted GCSE results are not based on fact, MPs say.
Pass rates were improving before Labour's extra investment, MPs say
Real-terms spending rose by 31.6% from 1999 to 2003, while the proportion getting the equivalent of five good GCSEs went up five percentage points.
In the previous four years, results rose by 4.4 points, while investment increased by just 3.4%, the Commons education select committee found.
Chairman Barry Sheerman said there was no proof more money had helped results.
He said: "The government has argued that its increased investment in education since 1997 has led directly to increased levels of achievement, for example at GCSE.
"Our report shows that it is not possible to demonstrate a straightforward link between expenditure and outcome in this way."
Later he added: "It is no good just putting money in without reform and without very carefully checking which policies add value over
time and which don't.
"Lots of resources poorly managed is not a recipe for success."
In last year's Budget, the government said extra investment since Labour came to power in 1997 had "resulted in a measurable improvement in standards", particularly in GCSEs and tests taken by 11-year-olds.
But the select committee report warns ministers to take "great care" in making links between investment and exam achievement.
The "evidence cannot be proved to support" this claim, it adds.
The MPs found that the proportion of students gaining the equivalent of five grades A* to C at GCSE had risen by 6.7 percentage points from 1991-95.
Real-terms investment in schools during the period increased by 11.4% - around a third of the rate for 1999-2003.
Shadow Education Secretary Tim Collins said: "These figures demonstrate beyond a doubt that without major changes to our education system, the extra funds will just be wasted."
Liberal Democrat MP Paul Holmes, a member of the select committee, said the government had "failed to produce evidence" that its funding had improved results.
The government spent £27.6bn on schools in England in the academic year 2002-3, compared with £20.9bn in 1998-99.
A Department for Education and Skills spokesman said investment went "hand-in-hand" with raising standards.
It had provided "record increases in teacher numbers, the new buildings and the classroom technology necessary to support education reforms".