There is no current evidence to prove that academies raise standards for all schoolchildren, according to a cross-party group of MPs.
In a new report, the Commons education select committee said it was too early to know how much the academies programme is helping to improve the nation's schools.
It also called for the Government to commission research "as a matter of urgency" into the impact the initiative has had on primary school results.
Academies and free schools are semi-independent state schools that are free from local council control. They have freedom over areas such as the curriculum and teachers' pay.
Academies were first established under the last Labour government, as part of a bid to improve standards in the most disadvantaged areas.
The programme became a flagship education policy of the coalition Government, which opened it up to allow all schools to convert to academy status.
The select committee's new report, which looks at the success of the scheme, concludes that it is currently impossible to draw firm conclusions about whether academies are "a positive force for change".
"According to the research that we have seen, it is too early to judge whether academies raise standards overall or for disadvantaged children," MPs said.
The group added that there should be caution about using evidence on academies set up before 2010 to draw conclusions about those established since then as the programme has changed and grown considerably.
"What can be said is that, however measured, the overall state of schools has improved during the course of the academisation programme," the report says.
It adds that the academies scheme has led to more competition, challenged council-run schools to improve and given local authorities an incentive to intervene quicker to deal with failing schools.
The committee goes on to warn: "There is at present no convincing evidence of the impact of academy status on attainment in primary schools. The Department for Education should commission such research as a matter of urgency."
Primary schools benefit from collaboration, with or without academy status, it adds.
Figures show that more primary schools than secondaries now have academy status - 2,299 compared to 1,884.
But academies make up a larger proportion of secondary schools, 60% of secondaries now have academy status compared to 13% of primaries.
The report also concludes that that while some chains - those running groups of academies - have been very effective in raising standards, others achieve worse results than other similar schools.
"What is clear is that the picture is highly variable across the country and in the case of sponsored academies, across chains. More information is needed on individual groupings."
Committee chair Graham Stuart, Conservative MP for Beverley and Holderness, said: "Current evidence does not prove that academies raise standards overall or for disadvantaged children."
"Going forward, the Department for Education (DfE) should be less defensive and more open about its implementation of the academies programme, producing a range of clearer and deeper information about the performance of academy schools, chains and sponsors," Mr Stuart said.
"It should also review the lessons of the rapid conversion of secondary schools to inform any future expansion.
"While some chains have clearly raised attainment, others achieve worse outcomes creating huge disparities within the academy sector and compared to other mainstream schools."
He added: "Nearly half of all academies are not part of a chain. By being 'stand-alone', these schools risk becoming isolated from others and as such as both less likely to contribute to others and less supported if they begin to fail. In future Ofsted should require evidence of effective partnership with another institution before any school can be judged 'outstanding'."
Education Secretary Nicky Morgan said: "This report recognises our plan is delivering what parents want - more chance than ever to send their child to a good local school.
"As a result of our plan, we have a million more pupils in good or outstanding schools compared to 2010, 100,000 more six year-olds able to read thanks to our focus on phonics, and an increase of 60% in the proportion of pupils studying core academic subjects at GCSE.
"Academies and free schools have played a vital role in this transformation by promoting new ideas and approaches, and helping to drive up standards in other local schools as a result."
Shadow education secretary Tristram Hunt said: "The cross-party group of MPs has issued a damning verdict on this Government's school improvement strategy. The report finds that under David Cameron there is no convincing evidence that schools policy has delivered improvements for children in England.
"Progress in our school system has been undone since 2010, restricting the opportunities and life chances of young people."
Dr Mary Bousted, general secretary of the Association of Teachers and Lecturers (ATL), said: "This report makes essential reading. It exposes the truth of the matter: this coalition government's obsession with school structures has not transformed educational standards.
"Academy status is no magic potion to transform schools. In pursing academy conversion the coalition government has neglected interventions which are known and have been proved to work. Too many schools are isolated and unable to learn best practice from one another. Regional School's Commissioners, recruited to secure more academy conversions, are pursuing a goal which is worthless in terms of improving the quality of education for pupils."