The original plan was to complete the programme by 2020
A multi-billion pound scheme to rebuild England's secondary schools was over-optimistic, poorly planned and has led to disappointment, MPs have said.
A report by the Commons public accounts committee says the Building Schools for the Future programme had created expectations it could not meet.
The government has pledged to refurbish or rebuild all 3,500 secondary schools.
Schools Minister Vernon Coaker said the MPs' facts were out of date and the scheme was now accelerating.
According to the committee of MPs, "the department was over-optimistic in its original planning assumptions for BSF, creating expectations for the speed of delivery that could not be met".
Of the 200 schools originally planned to be completed by December 2008, only 42 actually had been.
The department had hoped to deliver the programme over 10-15 years, but now expects it to take 18 years, with the last school completed in 2023.
This is not disputed by the government, but minister Vernon Coaker pointed out that the committee's statistics were out of date.
Since December last year - the end of the period considered by the committee - the number of schools where work had been completed had almost doubled to 78.
A further 115 were due to be finished in this financial year and the 200th school should be completed in the middle of next year, he said.
Committee chairman Edward Leigh, a Conservative MP, said: "BSF has been beset from the beginning by poor planning and persistent over-optimism.
"This has led to widespread disappointment in the rate at which schools are being completed, inevitably damaging confidence in the department's ability to complete the programme even by the revised date of 2023."
Centralising the management of the programme had had benefits, he said.
But the department and Partnership for Schools (PfS) - the body set up to manage the programme - must dispel the "air of complacency" which surrounded them.
They should indicate in detail how they proposed to speed up the pace of delivery and finish the programme on time.
"It's going to be a tall order to double the number of schools being procured and constructed."
Mr Coaker said: "By 2020, the vast majority of local authorities will have completed their programmes, with the remaining ones in the closing stages.
"The private sector has voted with its feet and is backing BSF despite the current downturn, with 20 financial institutions in the market and four PfI agreements closing already this year.
"But we've never been complacent about BSF. BSF is a completely unprecedented project, not a race to spend money.
"We've always been upfront about the early delays but we've listened and learnt lessons. We want value for money from every single penny of taxpayer's money - which is why we insisted that the early projects took far more time to improve their proposals.
"We've now slashed procurement time and costs and improved management on the ground so that projects are now being delivered on time and on budget."
A report by the National Audit Office published in February found that the BSF programme had been delayed by about 21 months. It also found that it was up to £10bn over budget.
The government estimates the whole scheme should cost up to £55bn.
PfS chief executive Tim Byles said the new report was like "looking at BSF through the rear view mirror, based on evidence gathered back in 2008" and the group's planning suggested the "vast majority of projects" would be completed by 2020, assuming continued levels of investment.
"In 2005, new targets were set and since then BSF has met or exceeded the target for schools openings.
"The National Audit Office stated that to deliver the programme by 2023, 200 schools must be in construction by 2011. Our detailed planning confirms that we will significantly exceed this, with 300 schools in construction by 2011, most of which are already under contract."