I haven't ever encountered any problems with performing at school. I perform at school when I get the chance, or if I feel like amazing people that day
. Yes, I have shown some tricks where some friends did know the secret, but it surely not because of Youtube, or because someone exposed it to them.
My best advice is to pick your audience carefully, which is what I do. However, it DOES constrict you to performing for fewer people and restreict you to some performing conditions, but I must say that this is better than having everyone know the method to your trick!
I usually perform to friends, or at least people I know will not search 'magic trick exposed' on the web. I once performed for a friend who knew the secret to 2 Card Monte (part of it at least), but since he was a good guy and my friend, he didn't tell anyone.
The type of people you want to perform for are:
Loyal Friends (ones who won't tell everyone the method)
Laid Back people who just want to witness magic.
NICE people.
People that you know will not look up secrets
Sorry if the list above is very vague, but I cannot really explain who to perform to. When I perform, I am never afraid of them looking up the trick- probably 'cause people in my school are awesome!