More than 300 primary schools across England have been forced to become academies in the last three years against a backdrop of mounting opposition from parents, a Guardian investigation has revealed.

Analysis of government data has shown that 314 schools were forcibly removed from local authority control after being rated inadequate by Ofsted. The Department for Education (DfE) has paid out at least £18.4m to academy trusts for taking on the schools.

Concerns are growing, however, about the stability of the system, with evidence that a rapidly increasing number of primary schools are being passed from one trust to another after conversion, causing long-term disruption and uncertainty.

Guardian analysis of DfE data shows that the number of primary schools transferred between academy trusts following conversion has tripled in just three years, from 39 to 121. Since 2013-14 more than 300 primary academies have been rebrokered or moved between trusts.

As a result, academy sponsors have picked up almost £4m in grants after taking a school from another chain, infuriating critics who point to the current funding squeeze in schools. Meanwhile, seven trusts running primary schools closed in the space of a year up to 2017-18, leaving their schools in search of another sponsor.

Quick guide Forced academisation of schools Show Hide What is forced academisation? “Forced academisation” describes how a state school in England is compelled to change its legal status from a school overseen by a local authority to that of an academy, and to accept new management by an academy trust. How is it triggered? Forced academisation is an order issued by the Department for Education (DfE). A school is forced to become an academy if it is “eligible for intervention” under law. The order is triggered by a school being classed as inadequate by Ofsted. Previously it could also be triggered by poor performances in exams but that condition was dropped by the education secretary, Damian Hinds, in 2018. Do parents get any say in the matter? No. Governing bodies, parents and councils get no input in the DfE’s intervention to force academisation. They also have no say in which trust the school is forced to join, meaning the chain may be based hundreds of miles away. Critics say this is a derogation of local democracy. What happens to the school? The school’s legal relationship becomes a contract between the trust that manages it and the DfE, cutting ties with local authorities. The school’s land and buildings are effectively leased to the trust. Head teachers are stripped of their autonomy, with budget and staffing decisions made by the trust. In most cases the school’s existing leadership is dismissed. The school’s governors lose legal responsibilities, and there is no requirement for trusts to consult with parents. Often the school is renamed and a new uniform adopted. The trust retains a proportion of the school’s funding for its administration and executive costs. Does forced academisation improve schools? There is little evidence either way. Previously, three-quarters of schools rated as inadequate by Ofsted later improved without forced academisation. The National Audit Office has concluded there is a lack of capable Mats able to improve schools in difficulty.

Commenting on the Guardian findings, the shadow education secretary, Angela Rayner, said: “This is yet another sign that the Tories’ academy system is failing even on its own terms. The problem of ‘zombie schools’, abandoned by failing academy chains, is spreading at primary level, while other schools are passed from to trust to trust, leading to growing instability.”

Academy trusts, meanwhile, are expanding rapidly as they absorb more schools. St Ralph Sherwin Catholic multi-academy trust in Nottingham saw the biggest increase, jumping from six to 20 schools in just one year, receiving an estimated £1m from the DfE in the process. Three of these were forced academisations.

Reach, one of the largest chains in the country, composed of Reach2 and Reach South multi-academy trusts (Mats), now has 68 primary schools in London, Birmingham, Essex, Kent, Reading, Hertfordshire, Buckinghamshire and Devon. Four have been rebrokered from other trusts, for which it received £220,000. This year, however, Reach2 was warned that it might itself lose one of its schools in Kent after an inadequate rating by Ofsted.

“A school system must be built on strong foundations and have the support of all stakeholders in order to thrive and succeed,” said Kevin Courtney, the joint general secretary of the National Education Union. “But, as each day goes by, the government’s academy programme is further exposed to be built on quicksand.

“Billions of pounds of taxpayers’ money has been spent on forcing schools into academy status, only to see those same schools being rebrokered further down the track as they are later failed by their sponsors.

“Some schools have had to endure multiple rebrokerings and a number of different sponsors, each bringing a change of ethos and approach, new school uniforms, a turnover of staff and a rise in exclusions and off-rolling. There is no stability in such a system and it is pupils, parents and staff who lose out.”

The majority of secondary schools in England are now academies, but primaries have been slower to convert. The proportion of primary school pupils being taught in academies is steadily rising and now stands at more than a third, at 1.6 million pupils, according to the most recent school census.

While schools judged good or outstanding by Ofsted can choose to become academies, since April 2016 if a local authority maintained school is judged “inadequate” the DfE will issue an academy order removing the school from council control and forcing it to join an academy trust.

A trust will be awarded a grant of £70,000 to £150,000 to cover conversion costs. If the school has a deficit when it converts, the council picks up the bill, which can be steep. Bradford council was left with costs of £250,000 when three primary schools converted to academy status.

The moves can be complex, critics say, creating a costly academy merry-go-round. Oldknow Academy, which was one of the schools involved in the Birmingham “Trojan horse” scandal, was rebrokered in 2015. The new trust, Ark, received £260,000 from the DfE for taking it on – the highest payment for a primary school in the dataset.

That school then closed in 2018 after merging with Ark Victoria academy to become an all-through school. Ark Victoria had itself also been rebrokered after its original sponsor, the Perry Beeches Trust, was closed after a government investigation into financial irregularities.

The DfE denied that the transfer of academies to other trusts reflects instability in the system. “Last year, only 3.3% of all academies transferred – most did so voluntarily, and this often involved standalone academies joining strong Mats,” a spokesperson said.

“There are over half a million pupils now in good or outstanding sponsored primary and secondary academies that typically replaced underperforming schools. In converter academies open for one year, 65% of pupils reach the expected standards in reading, writing and maths; this figure rises to 71% in converter academies open for seven years.

“We are striving for a world-class education for all children regardless of background, and when we see issues of underperformance we will not hesitate to take swift action.”

According to the DfE more than two-thirds of academy trust transfers were initiated by the outgoing trust, and about half involved single-academy trusts moving into Mats.

Rayner said the Tories had wasted money on academy conversions, while school budgets were squeezed year on year, leaving headteachers with little choice but to beg parents for donations. “Labour will end the Tories’ programme of forced conversion, re-empower local communities and properly invest in all our schools,” she said.

Courtney said: “The academy ship is sinking. The number of parent-led campaigns to defend their community schools should put ministers on notice that the academy programme’s days are numbered.”