Hi, I work for the British Humanist Association and we actively campaign against faith schools (for reasons of segregation, indoctrination, and curriculum (i.e. "some" schools teach creationism and do not believe in evolution)).
Anyway, with regards to some of the above comments. Yes some state schools kind of are secular, not by law... but they (thankfully) do not follow the law that every day must contain a session collective worship. Technically though, none are secular.
As for the league tables, there are a number of reasons. Mainly, as mentioned by some of you already, the schools are selective and not representative of the over-all population. There ARE less children from poor & disadvantaged families/backgrounds in faith schools (which is a disgrace in our opinion) as they don't make it through "selection".
Also, it does come down to the parents a lot in a self perpetuating, self fulfilling prophecy. Rather than attempt to explain it myself I shall take a quote from our site:
"Why does it happen? ? Explaining how religious selection leads to socio-economic selection
It is simplest to explain this by using an example. Let?s say there are two schools in a town ? one an inclusive community school, and one a religiously selective ?faith? school. Let?s say, for whatever reason, the ?faith? school performs slightly better (as one would expect it to some of the time).
It then follows that for many parents, it becomes more desirable to get their children into the ?faith? school. And more ambitious parents, typically from wealthier backgrounds, are likely to work harder to manipulate the system ? for example, by attending church when they otherwise wouldn?t ? to get their children into the stronger school. In other words, the selection process itself cuts out the pupils from the poorest backgrounds; and so the school ends up with more parents who will push their children to perform better; and so the school performs even stronger than its neighbours; and so the cycle perpetuates."
The whole article is at: www.humanism.org.uk/news/view/994
Finally, there is the issue that faith schools aren't playing fair in terms of competition. Again rather than explain myself, here is a link: www.humanism.org.uk/news/view/1029
I hope that helps.
FYI there is an interesting documentary of the subject here: www.channel4.com/programmes/faith-school-menace/episode-guide/series-1/episode-1
Plus there are a few other such documentaries out there if you're interested.