The estimated £5bn funding for the government's academy schools in England should be withheld until they are shown to be cost-effective, MPs have said.
Academies have cost between £13m and £38m each
Ministers were accused of lacking a coherent strategy and of rolling out schemes without proper evaluation.
The Commons education committee also criticised the admissions system, saying schools increasingly chose pupils, not the other way round.
The education department said standards
in schools had never been higher.
After a two-year inquiry, the select committee concluded it was "difficult to detect a coherent overarching strategy in the government's proposals".
The MPs welcomed the rise in standards seen in many specialist schools and some of the new academies.
But they said the reasons for success needed to be understood.
Good management and extra funding alone, rather than the specialising, might account for better results in specialist schools - now the "universal model" for secondary education.
Academies have cost the Department for Education and Skills between £13m and £38m each, whereas their independent sponsors put in 10% up to a maximum of £2m in return for control of the governing body.
The committee said this averaged £21,000 per pupil - often far more to begin with - compared to £14,000 for a new comprehensive.
Yet in the GCSE-level results for the first 11 academies, five had not improved and some had actually got worse.
The communities they served were "particularly vulnerable" and had suffered "years of inadequate education provision", it said.
So investment was welcome.
"But the government should ensure that the current programme of academies is thoroughly evaluated, both in respect of the performance of individual academies and the impact on neighbouring schools, before embarking on a major expansion of an untested model."
Schools Minister Stephen Twigg told the Today programme on BBC Radio Four the government wanted to learn from evidence about what was happening in the academies.
"There is some evidence that there have already been improvements," he said.
He said that it was not suprising that exam results at some academies were not good. They were usually in the most deprived areas of the country.
"Some are brand new schools and some replace existing schools which by their nature are failing schools which have been languishing at the bottom," he said.
The select committee's report also tackled admissions, saying ministers showed "startling complacency" on the issue.
The committee said: "The evidence we took during our inquiry indicates a troubling slide away from parents choosing schools for their children and towards schools choosing the pupils they wish to admit."
The government refused to acknowledge this let alone act to reverse it.
Indeed its proposals to give schools greater independence might make matters worse.
So the admissions code of practice should be given legal force.
The committee also found a "tension" between plans to give schools more independence, and the desire for them to work more co-operatively to share expertise and the disruptive pupils whose behaviour was driving teachers out of the profession.
Committee chairman Barry Sheerman said: "Whilst the strategy offers some welcome changes, it also contains much that has not been properly worked through."
But a spokeswoman for the Department for Education and Skills said: "The facts speak for themselves. Standards of education have never been higher, and continue to rise."
Academies were "making big strides in a very short space of time". Specialist schools were performing better, faster than other schools.
"We are committed to ensuring that every school is a good school, using choice and diversity to drive up standards, so that every parent will be satisfied with the school of their choice for their child."
Shadow education secretary Tim Collins said the report "highlights the appalling extent to which Labour has failed parents, teachers and children".
"After eight years of Labour failure, a new approach is clearly needed. The incoming Conservative government will make improved classroom discipline, academic attainment and school pride one of its top priorities."