The Government has handed over more than £18.6 million to schools to help them turn into academies, figures show.
Union leaders said it was a "waste of taxpayers' money" while one MP said the figure was "astonishing". The Department for Education (DfE) said the costs reflect the success of the academies scheme.
The academies programme was first established under Tony Blair's Labour government to boost standards in poorer areas. Last year, under the new coalition Government, Education Secretary Michael Gove opened up the scheme to allow all schools to apply for academy status.
Academies are semi-independent state schools, free from local authority control, that receive their funding directly and have more freedom over areas such as the curriculum and staff pay and conditions.
Schools applying to convert can submit an application for a "conversion support grant", a one-off payment of up to £25,000 to help meet the costs. The money is used to help meet legal and administrative costs, such as changing signs.
A response to a written parliamentary question asked by Lisa Nandy, Labour MP for Wigan, reveals that the total converter grant paid out so far is £18,642,779. In his response, Schools Minister Nick Gibb adds that "this is expected to increase as more converting schools are given grants to convert".
As of October 1, 1,031 schools in England had converted to academy status, while a further 495 had applied to do so, the written answer shows. It means that each of the 1,031 schools received the equivalent of just over £18,000 each.
Ms Nandy said: "It's an absolutely astonishing amount of money to spend on conversion. You have to ask the question whether this money would be better spent on all children and all schools rather than some schools and some children."
Christine Blower, general secretary of the National Union of Teachers said: "At a time when local authority and schools budgets are being cut, it seems an extraordinary waste of taxpayers' money that such financial rewards are being handed out to schools that are simply converting to academies. As these schools already exist it is baffling why the Secretary of State feels they should be given thousands of pounds."
A DfE spokesman said: "Schools becoming an academy incur costs for various things such as legal fees, carrying out consultations and buying new signs and stationery. As a contribution to these costs, the department pays them a grant of £25,000. This was made clear on the day the policy was launched, and the costs so far reflect the runaway success of the programme."