I didn't try asking over the phone - but if you do and you're successful, please let me know!
Graveney doesn't use the banding system. It takes a given number - around 60 I think - based on the test score, so to get in on ability you have to be at least in the top 5% or so. The rest are admitted as siblings and on distance from school.
Whether a child is put into extension or not depends on a lot of factors, I think, including the test score but also SATs and a test that they take on arrival.
Chestnut Grove uses the 'fair banding' system - the children are divided up into 5 ability bands and each band contributes 20% of its intake, with distance being used to decide who within each band is admitted.