It does, you have to be living in the catchment (or local priority area as they refer to it) to take the exam in the first instance.
Taken from DAO's website, the local priority areas are as follows:
Aldenham, Essendon, Northaw & Cuffley, Bayford, Hatfield, Potters Bar, Brickendon, Liberty, Little Berkhamsted, Ridge, Colney Heath, London Colney, Shenley, Elstree & Borehamwood, North Mymms, Welwyn Garden City
or any of the following London postcodes within the London Boroughs of Barnet and Enfield:
EN2 sectors 7, 8
N11 sectors 1, 3
N14 all sectors
EN4 all sectors
N12 all sectors
N20 all sectors
EN5 all sectors
N13 sectors 4, 5
N21 all sectors
It couldn't be spelt out any clearer in their FAQ's section, that if you live outside catchment, there's no point at all in applying:
- Can our child take the entrance and/or music exams even though we don’t live in the Local Priority Areas?
The allocation of places under oversubscription criteria 4 (Music) and 5 (Entrance Exam) is made only to children who have their permanent home address within one of the Local Priority Areas. Therefore, if your permanent address is not within our Local Priority Areas your child would not be invited to take our tests.
- So if I don’t live within the Local Priority Areas can I still apply to the school?
Yes you can still apply. Your application will be considered under any other applicable criteria (i.e. "any other child" - (criterion 8) which refers to distance from the school). However, as our application numbers are so high, it is unlikely that your application would be successful. Please refer to our Admissions Arrangements for full details.