hi there. firstly, never - ever think that a question is silly because if you don't know the answer then it isn't a silly question

(its only silly if you don't ask).
Confidence building and self-esteem is something that most definitely can be learnt. I think the key to this is setting small but achievable goals and work your way through and up.Once the first goals have been achieved, then set the next set. Possibilities are endless really it just needs the determination to do it). Perhaps you could start by writing down 5 goals onto a piece of paper and make it your priority to achieve at least one of them every lesson. Works wonders for the self esteem.
Example:
1. When stretching, join in the group. (start by just saying hello and then set to the task at hand - you may be surprised at the welcoming response you are bound to receive. it is just a matter of making that initial contact and you will find the common bond with other students can make class quite relaxing. great start)
2. Wear something that you would not normally wear to class. (step out of your comfort zone).
3. Dance like no-one is watching (here is where you can let down all inhibitions. you just may surprise yourself).
4. Aim to conquer that step that has been a problem. get your teachers to help you with this one.
5. Tell your teachers how you feel. enlist their help.
Perhaps a book kept in your ballet bag in relation to affirmations may also help.
Hoping this may be of some help. I do know how you feel. I felt the same when I gave my very first tutorial. i was absolutely petrified but I wanted to do it and and thought to myself that my students are only human. I am only human. if I make a mistake, so what. I practically forced myself to do the tutorial because I really wanted to do it. and you know what? I got up there, talked non-stop for two hours and I think when I walked out of that room, my feet did not touch the ground. i have achieved something that I thought for me was impossible. the tutorial was a success and i now have the confidence that I CAN do it and now can't to wait until I can deliver my next one. I think that you need to block out any negative thoughts that you may have against yourself and just think: if it is to be, then it is up to me, to make my dreams a reality.
So there you go, take a big breath and go for it. Please let us know how you get on. Head up, shoulders back, power on
