Leon co-founder and School Food Plan adviser John Vincent told BBC Radio 4’s The Food Programme that his taskforce reported to the government that there was an “ongoing structural issue” with having a small school.
He said: “All that needs to happen is that the funding formula needs to be a correct formula. It needs to be done in a way that reflects the reality of big and small schools.
"If 20p were to be taken of the per head costs of larger schools, and given to the smaller schools, the funding mechanism would work. It’s kind of baffling that such a straightforward change in the formula that would benefit small schools isn’t happening."
The Department for Education told the BBC: "We are not going to publish the Small Schools Taskforce report.
"It wasn't published last year because of the Spending Review and by the time that was complete, the report was out of date and much of it was already in existence."
Schools with fewer than 150 pupils received extra money under the UIFSM policy, which was then withdrawn as planned at the start of the year.