We've seen much lately about such huge youth conventions as Battlecry 2006 http://www.battlecry.com/ and others and was day dreaming whilst idling in bed this Saturday morning of an atheist rally of this sort.
I thought of a Royal Society christmas lecture writ large. With huge experiments on stage, pyrotecnics supplied by chemistry, an imax / planetarium style trip from the very smallest to the very largest reaches of the universe. From the world where quantum mechanics rule to the furthest reaches of our telescopes and beyond to the limit of our current theories. Then from a cooling proto-earth through the first glimmerings of life via the Burgess Shale menagerie onwards to the mega fauna (animatronic giant tree sloth anyone?) of more recent times and then our own history from the shores of an African lake to modern times.
Using all the multimedia available, lasers, imax, pyro, music, subsonics, video walls etc. this is not a scheme to educate in detail with long latin names and inpenetrable math, but a huge joyous sweep through science to get over the wonder, the magesty and the downright fun of living in this universe we find ourselves in and the pleasure of finding things out.
We could pin them to the wall with the wonder of it all!