There may be no better way to build confidence than through theater and acting. I've been writing and directing for a long time, and seen a lot of kids in the ten years I've been doing this. I've seen how involvement in theater and acting can change kids.
I'll tell you a story. There was a student years ago in 7th grade who was very shy and introverted, and her parents contacted me about getting her involved in the play I was writing. She was so shy that she didn't want to even audition. She had an interest in acting, but lacked the confidence you need to get up on stage.
When she auditioned, she did well enough to get an understudy role. Her parents were glad that she was at least involved.
Then one day as I was walking down the hall of our school, I heard someone playing the piano. As I got closer, I looked in the music room and saw the same girl playing this beautiful music, I mean unbelievable. I asked her where she learned to play like that, and she said shyly that she'd been taking piano lessons since she was four years old. I immediately decided to write a part especially for her where she could showcase her talent. I wrote a new scene that night, included her as a new character where she could play the piano, and we included it in the play.
Everyone saw a change in her. She was no longer the shy little girl who was too scared to speak loudly on stage. Her parents called me in shock later that week and thanked me up and down. They said she officially broke out of her shell, and they were so happy how she had grown.
The great thing about what we do is that it's all original. I often change plays and scenes and characters on the fly as we're rehearsing, and I revise constantly. This can't be done in a copyrighted play.
Okay, so what happened to that girl? She's 23 now and in NYU acting school. Somebody told me she's auditioning for Broadway shows, and won't stop until she gets there.