Been there. High school was a very dark time for me. I'm 28 now and working in journalism, where I talk all the time. It gets better, but it can take time. Hang in there, buddy. Push yourself as hard as you can. Build up that scar tissue. The thing is you CAN speak up in class already. It's embarrassing, sure, but you can do it. And the more you do it the less embarrassing it will be. However, your mom should really not be hitting you for stuttering. That's abusive parenting.