I totally disagree that the result would have been more impressive had it been in a coastal town. Just 15 years ago, London schools were at the bottom of the league tables. news.bbc.co.uk/1/hi/special_report/education_league_tables/32270.stm
APS is in Haringey which was second from bottom in 1997.
At that time, London schools were considered worst because they had high numbers of EAL kids. Now this is somehow cited as an obvious advantage compared to having native speakers.
APS has a very typical catchment, both for London and also the UK as a whole. FSM are close to the national average at 27%, they have a high percentage of special needs kids. Yes, some families will be middle-class, but so too are many families in the U.K. The richest will have opted for private and others grammars like Latymer which is quite close.
As a London parent (not APS), I find it heartening that a well-run comprehensive, with no selection, and where many will have shunned for grammar or private, can produce results that are as good as the best in the world. And yes, for a school like APS which is a comprehensive, a comparison with national averages is appropriate as it does not select its intake, and includes many disadvantaged children.
What APS does show is that well-run comprehensives can compete globally. The result is impressive. Full Stop. No need for qualifiers.