Now, there are many outlets for both that teen and their parents (and their teachers, and their friends, and their friends' parents) to say or do something in response. There are resources online that virtually anyone can access, phone numbers you can call, authority figures better-trained to recognize these problems. And perhaps most importantly, we got rid of the absurd mentality that what happens in other families is none of our business, no matter how many unexplained bruises or cuts we witness.
Only now that we are openly discussing and grappling with these issues do we have ay hope of turning the tide.