In addition to calling for more cash to meet massive demand, in its official response to a DfE call for evidence on SEN funding, the ADCS argues for a more central role for the public sector.
It is part of a raft of measures suggested by the association, which includes a fee cap to stem escalating costs of independent non-maintained special schools, and academisation of such settings to bring them into the state sector.
The response also highlights how up to 70 per cent of placements in independent non-maintained special schools are "tribunal directed", fuelled by a parental push for specialist facilities.
Growing numbers of learners are being moved out of mainstream schools into specialist or alternative provision, the ADCS claims, in a "worrying trend that risks two decades of progress on inclusion".
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Some individual packages are costing over £100,000 a year, which the response describes as "clearly unsustainable in the current context, adding that the "funding model for such placements is unregulated".
The "notional SEN budget", which requires a school to cover the first £6,000 of costs for each child, "can act as a disincentive to taking and/or keeping learners with SEND in mainstream schools", it warns.
Increasing costs have led to an eight per cent real-terms fall in funding in the five years to 2019/20, leading to a loss of classroom SEN support.
Parents no longer have the benefit of a definition of SEN support from the guides School Action and School Action Plus, says the ADCS, triggering an increase in requests for statutory education, health and care Plan (EHCP) assessments.
Latest government figures show that the number of learners with EHCPs increased by 35 per cent in the five years to 2017/18, with notable growth in the older cohort up to the age of 25.
The association warns: "Parents report being encouraged by schools to request an EHCP assessment as a means of unlocking additional support and/or alternative school placements if they cannot access SEN support.
"Conflicting pressures on schools to achieve high academic standards can act as an additional disincentive to some to be inclusive and can also act as an incentive to schools to seek an EHCP rather than a SEN support plan."
The response also goes on to highlight a shortage of special school placements, which it says is "driving greater usage of more costly independent placements" beyond home local authority boundaries.
It calls for all but the most severe or complex needs to be met locally "so children can stay within their local community, close to friends and family networks".
Referring again to high rates of tribunal successes by parents, it adds that a "strong emphasis" has placed on parental preference within SEN reforms, but that this was never sufficiently costed in the funding model.
"Going forward it is important to find a balance between parental preference and the amount of funding available in a locality," it suggests.
A ruling in a high court judicial review challenging the government's decision making over SEND funding, is expected in the autumn.
