Do you have recess? Do you know where she goes after school? Do you know what room number she is in? Maybe you could talk to someone that is in her class.
Be friends with a tom-boy in her class then have her tell your crush that you like her and if you wanted to hang out some time in the week or next week. Trust me, this is how I got my girlfriend.
if you really like her you will on purpose get held back and get bad grades but if you dont like her enough to do that then shes not worth it