Sibling rivalry is a whole different ball of wax with teenagers. It's not about who gets the doll. It's not about who gets the front seat -- although, that's still going on with my teenagers. I think at this age, when they are fighting, it is more verbal. I think that it's pretty mean. They find the weak spot in each other, and they just go for the jugular. As a parent, what I try to do is, sort of, be there to mediate. I try to let them work it out, unless it starts to get really mean, and one is taking the other one down. I do believe that once they've worked through, they are better off for it. It's painful, but that's, kind of, what siblings do to one another. Hopefully, they will grow out of it and get to be great friends, once they get a little older, and a little more mature.