Angry headteachers have confronted the Department for Education's funding group director over cuts they say are leaving their schools "on the edge of collapse".
Tony Foot was speaking at a Westminster Forum event on school funding today, at which the scale of anger and concern over stretched school budgets was made clear.
Ark's Evelyn Grace Academy faces having to cut "key staff" by 25 per cent by 2021, according to its chair of governors Richard de Friend, who was speaking on a panel this afternoon.
He said this could leave it with a student:staff ratio of 16.1, down from the current 12.5:1.
"For us as governors, the test will be: is it possible for our school to achieve some pretty challenging attainment - in enrichment, pastoral and safeguarding - objectives, with a reduction of 25 per cent of our key staff?" he said. "At the moment, I don't know to be quite honest."
Richard Slade, headteacher of Plumcroft Primary School in South London said his school was set to lose £246,000, despite the extra £1.3 billion of school funding announced by the government last year, and despite the fact he has already made wide-ranging efficiencies.
He said that further savings should be found from the DfE, instead of from school budgets.
He said: "The DfE is not fit for purpose and does not provide value for money. If the DfE were a school it'd be in special measures and the leadership would be seeking other means of employment."
He pointed to criticism of the department's financial management, including in the National Audit Office's examination of the first set of academy accounts, published last autumn.
Mr Slade asked Mr Foot in a later session whether he recognised that the DfE was unfit for purpose and was failing to provide value for money.
Mr Foot responded: "I hope what's come across in this session was how sensitive this process [the NFF] was, and the evidence that underpinned it."
Asked whether the national funding formula would work without additional money, Mr Foot said: "It's really important we're getting money to areas where it can do the most good, particularly in times that are more constrained.
"It's about making sure that every pound we've got available in scohol funding is doing the best it can."
Meanwhile, Grahame Robson, headteacher of Manor Green College, a special school in West Sussex, repeated warnings he first made in Tes, that he is having to send pupils home due to cuts to the high needs budget leaving him short-staffed.
He called for "interim funding" for schools that the DfE "knows are on the edge of collapse". "Schools like mine do not have time to wait," he added.