How do i boost my self-esteem and confidence?

ok, well i feel really stupid, like my brother is super smart literally he has 99s and 100s on his report card and he aces everything, as for me, i don't. i have to work hard on things and right now i'm studying for the PSATs and in the math questions, i don't know anything. in the 2010-2011 school year i will be a sopre and do u think that when i go back to school that i will improve? thx everyone! :)