I can see why cgehansen wants to explore the merits of some kind of catchment based system; and I can also see why tiggy does not think they would help in London.
I would suggest that there are two seperate issues here:-
1.What improvements can be made to the current system?
and
- Would a completely different system be better?
Under 1, improvements, I think there seems to be a general view emerging on the thread that a sharp restriction or even abolition of sibling preference would be a help. I would agree with that as a policy and its one worth pushing with the council as any system that facilitates deliberate "gaming" by way of shor term renting distorts the pattern of demand. So if, as is rumoured, there are short term renters whose real base is Wood Green but who rent beside Coleridge in the block of flats on Crouch End Hill, then the radius of Coleridge is indeed being reduced by non local parents doing this which makes demand in Crouch End look higher and demand in Wood Green look lower.
I would, controversially, go further with Church Schools.
It seems to me that if Church Schools were to be given the option of explaining very clearly what their ethos was, and the extent to which pupils would be expected to go along with it, then parents would be self selecting, and consequently admission to Church Schools could be done on the same basis as community schools - special needs, then distance. This would again avoid distortion of local demand, and mean that church attendence etc would cease to be part of admission, a feature of the system I really dislike. But perhaps thats just me.
I will leave proposing a different system to a later post, cos, while I am interested in that, I think its a bit academic at present.