Yes, that is what the forums are for, advice.
I'm going to say that if you have done any close up work at all, in your elementary school and such, then you already have some experience. Wait...elementary....did you mean middle school as that is what is right before high school....perhaps? Either way.
High school isn't much different, except that you hope everyone is becoming more mature and getting into their "older" stages in life. There will be different kinds of people to experience and they will react differently perhaps than the younger kids you have performed for before. Most any of the street type close-up effects you do will work in a school setting as well. All your basic main stuff, but if you ARE going to be doing it daily (as I sometime have for weeks at a time before for various people) then you will be learning the nice new skill of improvisation. Learning to string together sleights, colour changes, moves, and everything else you have learned over this time into new effects you've never seen, and even if it's just basic they will think it's a whole new "trick". Run through the list of effects in your head that you have down, think who you are performing for and what you have shown them before (that's hard to remember and was my only problem usually) and then pick something, go into your routine and do your thing.
Teachers or other "authority" figures try to take something away, offer your cards freely, do a deck switch for an empty box with something heavy in that is similar in weight to a deck of cards, or whatever else you think of. Personally I have extra decks in my backpack, they cost what...2 dollars a piece? Big deal. You are the magic, your personality and the way you present yourself, you are the magician. Don't let someone intimidate you just because they want to take your deck, act like it's no big deal and move on....do more magic later. I've personally had the principal walk up in the middle of an effect and slip my deck out of my hand and go back to his office, soon as he left I pulled out my other deck and finished what I was doing. Be polite though, and don't get offensive if they ask nicely. Perhaps ask to finish that one routine and then move on, and try to avoid it in that person's class especially.
All in all, high school is a fun place to get experience for real world things, but yes do remember you see them everyday for four years or however long. So anyday you are going to do some magic, be prepared and treat it as a performance, not a quick trick for friends. Don't get overly cocky and act better than the other kids just because you have this special knowledge. (you may feel over them, just don't act it.) Also, it's best not to make them feel extremely stupid....they are still younger kids like you whose self esteem etc. can be hurt easily and they may take offense or just be hurt by something ignorant.
(if you do a bill change into a lower denomination make sure they understand they will lose a bit of money and that is the fee for doing the effect).
If you have a certain personality and you use it during magic, the rest of school must be presented like that. Live your character. I am who I am during performance, and in real life just so that there is not a discrepancy.