Yeah, I was probably 12 or so when mum told me I needed to start using deodorant because the wet marks on my shirts went all the way down to my elbows... I had never even noticed :/ She used to buy me those icky roll-on things that just stay wet all day and mingled a powder scent with BO - gross!
There are some great stick deodorants out these days, I always go for ones with 'no white marks' (I wear a lot of black, but I also find it's great with white or coloured shirts as you don't get that residue everywhere) and I think Dove is quite nice - it keeps me pretty dry (I actually use it in combination with the Rexona Clinical Protection because I sweat like a huge dude even in winter :/ ) and smells nice. It won't get confiscated and won't be all sticky and wet... but from memory aerosols like Impulse were 'banned' at school too and every single girl I know had at least one can in her backpack! You just don't do dumb stuff like spraying it in front of a teacher lol, and if you walk into class reeking of it, just say you borrowed it off a friend HTH!