To be fair to schools, the old system gave the impression that they 'only' got money for some types of SEN. It worked like this:
School budget £100,000
SEN devolved budget: £20,000
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Total available £120,000
Then, schools were told this:
"Some SENs are very commonplace. We call these SENs 'High Incidence'. This means that any school could and should expect to have some children with these SENs at any time. We have factored this into the devolved SEN budget, so those children will not attract any money from the LA. These SENs include SpLD, EBD, SLI, MLD, etc.
Some SENs are less commonplace. We call these SENs 'Low Incidence'. The incidence is less predictable across the LA so we will fund those separately. Those SENs are, for example, CP, VI, HI, etc.
A child with a high incidence statement who has severe needs, requiring over 15 hours TA support per week will be funded by the school up to 15 hours, from the devolved SEN budget, and will receive a top up from the LA"
Schools then got the message that some SENs 'didn't come with any money' when in fact the money had been given via devolved SEN budgets.
The tricky bit comes here:
SEN funding was not ring-fenced. The devolved budget was notional - that means that a formula was used to derive the budget, based on the area the school is in, the pupil numbers, etc.
If a school had, say, £10,000 in their devolved SEN budget, but only had 1 child with mild SEN, taking £1,000 of resources, then they had £9,000 spare to pretty up the flowerbeds.
Now, they've tried to level the playing field. MS still get a devolved (notional) SEN budget. Out of it schools must pay the first £6000, regardless of how that £6000 needs to be spent (TA time or resources, equipment, etc.)
Special Schools get £10,000 per pupil (So the £4000 place cost, as MS, and the £6000 initial statement money) because they don't get a 'notional' SEN budget, as it's accepted that all the pupils have SEN at statement level (it's a requirement of a place). Then, each pupil is audited to see if they need a top-up amount in addition to the £10,000. DD1, for example, is likely to only get the £10000 as she doesn't have huge physical needs, no adaptive equipment, MLD and is well suited to the teaching style so doesn't need 1:1 or 2:1 for behaviour, etc.