Thanks. Ds didn't seem to mind the prep time at any stage - gradually increasing it in proportion to his increasing desire to compete worked well.
I wouldn't assume every group of 'mathletes' would necessarily qualify as 'nerds', so don't let my comment make you hesitate! Check out the available groups in your area - if you can meet or at least eyeball the kids, maybe you can get a feel for how welcoming they'd be.
And hey, it sounds to me as if the world of middle-school math competitions could use more girls (not to stray into the gender topic - that's another thread!): one of ds's best 'nerd' friends, a girl, returned from MathCounts Nats in May reporting that out of the 224 students competing, fewer than 50 were girls.
