So, do all children have to take the test to get in and is this done in the school itself, not their primary school
Yes to both questions.
Do other secondaries in the area also have an entrance test
Some other secondaries in the area use fair banding but not all of them.
Is it really possible to establish fair entry criteria if different schools have different methods for deciding what they think is fair
All have to comply with the Admissions Code and must consult with, amongst others, the LA. I believe the answer to your question is yes.
And who is the final arbiter of whether an admissions process is fair or not
The Schools Adjudicator.
And who checks up on it and how often
Every time admission arrangements are changed the school must consult with a range of people then submit their proposed arrangements to the Adjudicator for approval. The Adjudicator does not conduct detailed checks of all proposed arrangements but will investigate if they receive any objections. In terms of whether or not a school is complying with its arrangements, this is policed by the EFA (for academies) but is reactive rather than proactive, only getting involved when parents complain. If a school is found to be seriously in breach it can lose its funding.
And if house price premiums are the reason for the 10%, then why only 10%
I thought you wanted the school to serve its local area. That is why 90% of places go to pupils living within 2 miles of the school. That is a pretty big area - 12.5 square miles.
Is the system chosen not a little bit confused as to what it is trying to achieve
No. It is designed to ensure that the ability profile of the pupils admitted broadly matches the profile of pupils applying in terms, that pupils living locally (i.e. within 2 miles of the school) are prioritised and that parents cannot gain an advantage by buying a house in the streets around the school.
minifingerz
I note that the blogger ignored the fact that other Harris academies in the area using the same admission arrangements had high proportions of SEN, EAL, FSM, low achieving pupils, etc. I would love to know how the blogger thinks the school was managing to filter out non-statemented SEN pupils, EAL pupils and FSM pupils without knowing who they were - schools are not provided with that information prior to admitting the pupil.
Fair banding ensures the profile of the pupils you admit matches the profile of pupils applying in terms of their potential. It does not mean the profile will match in other respects. You may get more or less FSM pupils than the average for the area, for example. It may be spectacularly more or spectacularly less. If you have 100 pupils of whom 40 receive FSM and you randomly select 10 pupils repeatedly you will end up with 2 or fewer FSM pupils roughly one in six times. Every so often you will end up with no FSM pupils at all. That doesn't mean anyone is fiddling anything. It is what happens when you conduct a random draw.
Unless you fiddle the random draw there is no way a school can use fair banding as a covert means of selection. That is why the draw must be independently supervised.