We homeschool..... so I can't speak to how the schools do it, but DS can do whatever competitions he's interested in.
We've never done the online classes... I imagine they'd be useful whether you compete or not, but I can't really say for certain. I coach two math teams myself and I know that what I teach (aiming for the competitions) is broadly useful stuff. We don't spend much time at all on "tricks" -- however if I were teaching a Real Math Class, I think I'd spend more time than I do with these groups on proving our methods. It comes up, but it's not the main focus the way it is when it's just DS and me and the math book. That would be my one hesitation about recommending competition-prep classes... I'm not sure how thoroughly they go into the why.
