In 1950s, researchers discovered that children who passed the 11-plus had more dosh per pupil than those who didn't.
After academisation, pupils excluded (so that academies can 'improve') go to cash-starved local authority.
Same as 1950s.
Note: many arguments swirl around about selection, grammar schools and social mobility but this inequality in provision is rarely mentioned. What is emerging from the plans for academisation, is that this kind of unequal funding is on the way back.
Picture the local authority of the future, with a skeleton staff of a few people responsible in a purely administrative (not educational) way for getting everyone into a school. They have no legal power to force an academy to take a given child. They are essentially like beggars knocking on academies' doors on behalf of excluded and SEN children. Then the more that the local authority comes to provide by way of cheap, pupil referral units and the like, the more the academies will be able to wash their hands of these children.
But at the core of it, will be a lack of cash. These children will get less per pupil than those in the academies.
This is unequal, unfair and has to be fought.