My son actually got great grades in honors classes all the way through 11th grade. His senior year, this last year, he knew all he had to do was pass English to graduate and he did with an A. Other classes, not so much, but this school year was the start of his "disorder" getting completely out of control. Even though I'm a teacher, I have never focused on grades because they are so subjective.
And yes, my son's rages are frightening, too. Luckily, I have learned so much from the wonderful people on this board and I told my son that we could not live with him like that. I think he knew I was serious and he has tried his best to control his emotions. I have also worked on myself and am trying to stop engaging. I know that has helped, too. I can't imagine kicking my son out, but I also can't live the way we were living.