School leaders have warned that a proposal to spend £5 billion on catch-up vouchers for parents is "completely impractical".
The idea was announced during Liberal Democrat leader Ed Davey’s speech to his party conference.
Mr Davey said the plan would form part of a £15 billion recovery package with parents getting vouchers worth £200 per pupil, which they could then decide to spend at their child's school.
However, headteachers' union leaders have questioned how this idea could work in practice or be measured afterwards.
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Geoff Barton, general secretary of the Association of School and College Leaders, said: “While we understand that the proposal for a scheme to provide vouchers to parents as part of an education recovery plan is well-meant, it is also completely impractical."
It would not be possible to purchase bespoke provision from a school for an individual child in this way, he said.
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This was because schools have to organise academic provision and extracurricular activities on the basis of their overall budget and their assessment of what would most benefit their pupils.
He added: "They would not be able to provide, for example, an after-school football class for one pupil, and an after-school music lesson for another pupil on demand.
“Such provision might, of course, be available as part of a school’s overall curriculum, budget and staffing permitting, but it simply wouldn’t be possible to individualise this in response to a voucher scheme."
He also stressed the importance of keeping any education recovery programme "as simple as possible in order to make it easily deliverable".
Paul Whiteman, general secretary of the NAHT school leaders’ union, supported the Liberal Democrats' call for a £15 billion catch-up plan for education, pointing out that this followed what the government’s recovery commissioner, Sir Kevan Collins, had recommended.
But, he added: “However, we believe that recovery funding should be directed to pupils through their schools because they have already begun this crucial work and are well placed to further expand it so that every pupil gets the support they need.
“Furthermore, the school route means that the government would be better able to judge the impact of this investment because there are already well-established mechanisms for tracing school spending."
In his speech to his party’s conference, Mr Davey suggested the scheme could be “the world’s biggest-ever parent-listening exercise” with schools and government having to take account of their views.
“Parents could choose to spend it with their child’s own school – on an after-school homework club, on one-to-one tuition, on special extracurricular activities from sports to music lessons, provided for that child by their school,” he said.
“Or parents could choose to spend it on tuition they organise. Or with a music teacher they find. Or on therapy and counselling.
“As long as it was supporting the education and wellbeing of their child, it would be the parents’ choice.”
The Lib Dems said that under the proposals, catch-up vouchers worth £200 a year would be given to parents for all 8.3 million children in state-funded schools.
There would be double vouchers, worth £400, for disadvantaged children, and triple vouchers worth £600 for pupils with special educational needs.