Teaching unions have said that rising number of pupils who need extra support is putting more pressure on schools.
Paul Whiteman, general secretary of the headteacher's union the NAHT said "despite incredible efforts" the current system is "completely unsustainable".
He said "schools face shortages of experts like educational psychologists and speech and language therapists, and a postcode lottery in accessing additional money from cash-strapped local authorities for pupils with the greatest needs - while parents are having to take councils to tribunal to get the places they want for their children due to a lack of capacity".
More parents are turning to tribunals to challenge the support on offer for their child. Separate statistics out today from the Ministry of Justice show there were 24,000 SEND (Special Educational Needs and Disability) tribunals brought in the year to April, an increase of 36% on the previous year and the highest number on record.
The National Audit Office said in a report last year that the SEND system as a whole "wasn't financially sustainable" and wasn't delivering better outcomes for children and young people, despite big increases in high-needs funding over the last 10 years. Local authorities are under huge financial pressure because of rising SEND needs. A deal holding £3bn of SEND deficits off local authorities books is due to run out next year.
Tim Oliver, chair of the County Councils Network, said councils were facing a "financial cliff edge" if the deficits did land in local authorities' accounts, "potentially rendering half of England's county and unitary councils insolvent overnight".
He said councils needed "urgent clarity on how government intends to manage these deficits".
The government said in the spending review they would be setting out their long-awaited plans to reform the SEND system in England this autumn in a government white paper.
They've also set aside £760m over two years to reform SEND from a transformation fund
In response to today's figures for SEN pupils and the rise in SEND tribunals Education Secretary Bridget Phillipson said: "Behind each one of these figures is a family desperately fighting for even the most basic support for their child, leaving a staggering number of parents exhausted while young people are denied precious help.
"It doesn't have to be this way, and this government will deliver the reform that families are crying out for through our Plan for Change – giving an excellent education to every child.
"We have already taken the first steps to identify and meet children's needs earlier in mainstream schools, including through more early intervention across speech and language, ADHD and autism to prevent needs from escalating and £740m to encourage councils to create more specialist places in mainstream schools."
Additional data reporting by Harriet Agerholm