Not only do they often win, and almost always come in the top three, the kids at those competitions are MUCH BETTER BEHAVED
It’s not just a matter of expectations at school, it’s also greatly influenced by the home environment. I would bet that the majority, if not all, of these kids share the same last name with mom, as well as dad. Dad has a full time job, and possibly mom as well. Live in a single family home. And so on..