A move to turn all schools into academies risks the closure of small and “expensive” rural schools, as academy trusts avoid or try to shift the “less attractive” institutions off their books, it has been warned.

The government wants every school to become an academy by 2022, but the financial viability of smaller schools as part of a fully-academised system has been called into question by trade unionists and policy advisers with close links to the government.

Small schools already face a harsh financial climate because of low pupil numbers, and are often propped-up only by costly intervention from councils. The National Association of Small Schools is among those to have warned about an increasingly dire situation faced by its members.

But the issue is back on the agenda after the Association of Teachers and Lecturers tabled a motion to its conference next week, calling for an investigation into small-school funding.

Mary Bousted, the general secretary of the Association of Teachers and Lecturers, said the viability of small schools in academy chains was a key concern for union bosses and all parents with pupils at small schools should be “highly concerned” about their future.

“A multi-academy trust is essentially a business venture, and they have to be viable,” Dr Bousted told reporters yesterday. “I think any parent of a child in a small rural school should be highly concerned about the potential for that school to be wrapped up into a trust and then closed.”

Dr Bousted said smaller schools should stay under the oversight of councils, and warned smaller communities risked becoming “dormer villages for second homes” if they lost their schools, which she said were often a “centre for the community”.

But warnings about the future viability of small schools aren’t coming only from those who represent the schools and their staff. Jonathan Simons, the head of education at right-leaning think tank Policy Exchange, and a key player in government schools policy, has also warned that trusts could engage in “adverse selection”.

In a blog post, Mr Simons referred to the 1,975 primary schools in England with fewer than 100 pupils and the 113 schools with fewer than 30, admitting they could be considered “less attractive”, along with schools with high levels of debt or complex PFI structures.

He said: “In public policy theory, this potential for adverse selection by providers is referred to by the elegant phrases of ‘cream skimming’ or ‘dumping’, and it’s an accepted function for regulation to ensure that this is corrected for.”

Mr Simons said potential solutions included requiring new learning trusts or “local authority spin-outs” to be a provider of last resort, requiring regional schools commissioners to form an arms-length trust themselves to run unwanted schools, or a duty for trusts to take a “mixed portfolio of schools”.

Earlier this month, Schools Week reported that a series of small-school closures or threats of closure had left one Devon family having to move their daughter for the fourth time.

Becky and John Whinnerah will have to find another school for Tia, 9, after Sutcombe Primary, in the borough of Torridge, was earmarked for closure by Devon County Council. The school is less than half-full with just 21 pupils on roll, and has been unable to afford a headteacher.

A Department for Education spokesperson said it was “irresponsible” to suggest small schools would close as a result of its plans.

“As we make every school an academy, we will encourage them to work together in multi-academy trusts so they share resources, staff and expertise, driving up standards, and, in many cases, better support the sustainability of smaller schools,” she said.

She claimed that the new national funding formula would make funding fairer and would include “extra funding for small schools in sparsely-populated areas”.