Interesting post, trembletoe. I sponsor a semi-official club at a high school in Arkansas. The group is entering its fifth season. On average, the club has about 10 hardcore members from year-to-year who are primarily d20 and Magic players. The rest come and go. We meet once a week for a few hours after classes end. The club is mainly advertised by word of mouth, and I have not pushed recruitment too hard.
The students this year want to become an official school club; so, we are begining that process. I would prefer that we remain, as Obi-Wan might say, "free of Imperial entanglements." You mention that students drop out around report time. I am curious as to how you deal with grade and school discipline issues. I would hate for bureaucracy to strangle the joy of the game if the club becomes legitimate.
It is nice to know that other groups exist. Perhaps enough to form a network?