Well, as a child I went through the usual CoE experience that someone growing up in England, going through the public school system, and taking part in the Scouts (don’t know about today or other people, but my branch of the Scouts had mandatory Christian services at least once a month). However, I don’t think any of it really sunk in; certainly at the age of say, seven I was POSITIVE that there was a God (of the big-beard-in-the-sky) variety, but by, say, 13, I was completely atheist. I guess I never really found any evidence for God, plus the lack of any real religous vigour in either my household or my church may have helped (parents are very lapsed Catholics, and Anglican churchs are really more social gatherings than deeply religous institutions). Had I been brought up, say, Pentecostal, I might well have kept my faith until my mid-teens.
Around the age of 15 or so, the really ridiculous aspects of Christianity began to sink in, however (not helped by a few fundamentalist aquaintances, including one Creationist), and I really started to not believe in earnest. I suppose it was then that I became a “practising” Atheist, rather than one born simply of apathy and lack of exposure to genuine religous feeling (not to knock any Anglicans on the board, but most of those I know are of the tea-and-biscuits variety)- by that I mean an atheist due to philosophical conviction. I don’t want to derail this into a debate about the existence of God, so I’ll just leave it as saying that I have never seen a convincing argument for either the existence of God or of a Christian god.
I noticed that most of my friends went through a similar experience about that age, either becoming Atheists, staunchly religous in their already-practised faith (Confirmation, whatever) or converting. Make of it what you will.