MPs have questioned Chancellor Gordon Brown's Budget pledge to raise state school funding to the levels enjoyed by the independent school sector.
Mr Brown was praised for his pledge in this year's Budget
Mr Brown said he wanted funding per state school pupil to rise from £5,000 to £8,000, as in independent schools.
But the cross-party education select committee said the pledge amounted to an aspiration rather than a definite commitment with a specific timescale.
The government responded saying it had rectified decades of under-investment.
The select committee's concerns echo those raised in July by the Institute for Fiscal Studies.
The institute said the lack of a date on Mr Brown's aspiration "left us little the wiser as to the outlook for spending per pupil".
It estimated that it would cost £17bn to close the gap and that this would not be achieved before 2014.
No comprehensive information
As well as criticising Mr Brown, the select committee's investigation into government funding for education criticised the Department for Education and Skills (DfES) for producing an annual report that failed to provide any comprehensive information on education spending.
"Given the increased level of investment that this government has made in education, it is unfortunate that it has not yet proved possible to measure the effectiveness of that spending in providing better education and more highly qualified students," the report said.
"There is a risk, in the longer term, that the inability to demonstrate a measurable link between inputs and outputs will mean that taxpayers have no way of judging whether or not public resources are being used well."
A DfES spokesman said the department had already agreed to work with the select committee on the format of the annual report to address their concerns.
"The government has already invested record amounts in the education system, rectifying decades of under-investment," he said.
"Investment in education is a key priority for the government. By 2008, spending per pupil will have more than doubled from £2,650 to £5,750.
The government says it remains committed to improving funding
"As the Chancellor said in his Budget speech, the government's long-term aim is that, adjusting for inflation, we raise average investment per pupil to today's private school level.
"That position remains unchanged."
But the Shadow Schools Minister, Nick Gibb, said: "This is a very serious criticism, by an important Commons committee, of the Chancellor and the DfES.
"If we are serious about raising standards in schools we have to work on the basis of full and accurate information.
"The committee rightly highlight the fact that over-spun data and ill-defined aspirations confuse the debate and do nothing to help the nation's schoolchildren achieve their full potential."
Dr Mary Bousted, ATL general secretary, said the select committee should not "get hung up" on the lack of research evidence linking funding to productivity.
"Voters will judge the government on the quality of their local school buildings and the quality of learning shown by their children, and not by a spun research report," she said.
"Neither should the select committee get hung up on the need for an understandable funding system - understandable is simple, and simple is inequitable in a huge service meeting complex needs."