Aaaaah...I have been in the exact position you are now **sighs reminiscently**
Erm... maybe you mean that serious mental magic won't work for
you, and spongeballs will work for
you?
Because I think teens will be much more up for mentalism or mind-reading and stuff like that than...spongeballs.
Of course, it is always better to do what you are comfortable with and a cool spngeball routine will win over a boring mentalism one any day.
However, my suggestions will be DON'T DO CARD TRICKS unless they are srsly visible.
And try to involve anything which can improve the visibility of your effects.
And be very gutsy, don't hesitate to do the unusual and invade personal space of a volunteer IN A POLITE MANNER.
Unless you feel that calling a volunteer will be too much for a routine under 5 minutes?
I feel you should go with whatever you are best with. You can try a new effect, but do not try to learn a new sleight. The time period of one month might be enough to get a sleight smooth, but not enough to give you confidence of hitting it naturally and you don't shaking hands on-stage.
Am not actually suggesting effects because I feel you can get those pretty fine. But ultimately you will realise that the best are those you are familiar with and are confident. Your main attention should be more on the performance itself since you are not very used to stage magic, because stage magic and close-up magic are two different ball-games.
