It might not be doing the school a favour, since the funding formula is per-student.
But it's certainly doing the state a favour. There are 8.8 million school students, but the state only has to pay for 8.1 million to be educated (the children's own parents pay for the rest.) The state per-student education budget is £7460.
Since 8.1 million x £7460 (Current student numbers) is lower than 8.8million x £7460 (if all kids were in state schools), this means the state pays less than it would if we didn't educate our children ourselves.
And since all state funding comes from taxes, and whatever comes in is shared out between all state expenses - such as education NHS, welfare, pensions - then reducing stare education spending is doing every UK citizen a favour.
I find it really weird that some people don't understand that. It's obvious, surely?
Now here's the really good bit. The per-student education funding formula is set by the government. The government can choose to change it.
The UK spends £116 billion on those 8.1 million kids currently. If school numbers fall by 4.5% in the next 5 years as expected, the government could:
a) Increase the per-pupil funding so that the £116 billion is shared between the remaining 7.7 billion students. The teaching ratio would then change 1 teacher to 17.2 kids to 1 teacher to 16.4 kids
b) Encourage half the kids to move from private to state so that the education budget remains the same £116 billion, and still with the current higher teaching ratio. Oh, there will be an extra 1/3 of a teacher per school in the most optimistic case...doesn't really change the teacher ratio.
Which is better for the state kids (for the same overall education budget): a teacher ratio of 17.2 (with VAT) or a teacher ratio of 16.4 (by doing nothing)?
It's not hard to see which is better. But somehow, it's still beyond Labour's maths ability.