Every school in England will have pound;100,000 more spent on repairs and maintenance this year than those in Wales, according to the Welsh Local Government Association.
The gulf between the two nations' capital spending was revealed in evidence to an all-party committee set up to investigate the funding fog in Wales.
The WLGA said its research showed an average of pound;190,000 is being spent in every English school in 2005-6, compared with pound;90,000 in Wales.
It said local authorities needed to know more about the resources available to increase capital spending if they were to cope with new initiatives, such as the foundation phase and 14-19 learning pathways.
Concerns over capital spending led to opposition Assembly members winning a vote against the minority Labour government this week.
The Welsh Liberal Democrats pushed through a motion calling for an independent assessment into the cost of making schools "fit for purpose" by 2010. Peter Black, Lib Dem chair of the education and lifelong learning committee, said present estimates of the bill fell short because they were based on out-of-date surveys of schools.
He said: "I have been in schools where wind and rain are coming through badly-fitted metal windows, where flat roofs are in need of replacement and ceilings are coming down. This all has an effect on a child's education."
Chris Llewelyn, head of lifelong learning, leisure and information at the WLGA, said the Assembly had pledged pound;1 billion to help make schools fit for purpose by 2010.
But the target was in doubt as cash-strapped local authorities struggled to finance the huge amount of work needed on schools.
The Assembly government is making pound;560m available to local authorities over a four-year period through the School Building Improvement Grant, with the remainder expected to come through local authorities'
general capital allocations.
It says that pound;143.561m has been pumped into improving school buildings in 2005-6, and the same level of funding is expected until 2010.
However, the amount is under review, and AMs on the education and lifelong learning committee will not receive a decision until early next year.
The WLGA claims comparisons between English and Welsh capital spending are difficult because of complexities and differences in the system.
The association believes the vast disparity it has uncovered is accurate and points out that its calculations have not been contested by anyone.
Mr Llewelyn, from the WLGA, said: "The Association is concerned about the level of understanding over what is regarded as 'fit for purpose' in Wales and the extent to which the foundation phase, moves to community-focused schools, the 14-19 learning pathways, post-16 planning framework and falling pupils numbers will have an effect on this."
Christine Chapman, deputy minister for education and finance, said: "To achieve the 2010 target it is essential that local authorities use appropriate amounts of their own resources to invest in school buildings."
Geraint Davies, Welsh secretary of the NASUWT teaching union, said an independent assessment, with a final figure for making schools fit for purpose, was urgently needed.
Hel ne Mansfield, headteacher at Croesyceiliog comprehensive in Cwmbran, said some Welsh schools needed to be brought up to 20th-century standards - let alone the 21st-century.
Janet Ryder, Plaid Cymru's shadow education spokesperson, said: "Huge investment is needed to ensure our schools are equipped to meet the demands of the national curriculum.
"It is not just Victorian schools that need updating. Some Welsh schools built in the 1970s are in a worse state."
Opposition AMs also won a vote on a further motion to have ring-fenced grants to small schools. This, according to the Lib Dems' motion, would end the practice of including the costs of the workload agreement in overall school funding.
However, the Assembly government claimed it was already doing what the motion proposed.
A spokesperson said: "On school buildings we will be continuing with the work already in hand to assess what investment is needed, which is over and above what the opposition is asking for.
"On funding for small schools, we will continue with action to bring together in the budget for 2006-7 the elements of specific grant funding for small schools."