What do people see in this?
I spent most of the movie the same way I spent most of my 15th year: with my eyes closed, mumbling "make it stop, make it stop!". Had an exit not required slipping past the director I would have taken that option.
If you take your normal 15yo boy, put a camera in his face and ask what he's thinking, he will say "nothing". Maybe goof for the camera if you're lucky. Billy is no different except his condition prevents him from censoring himself. It could fairly easily be argued that Billy's thoughts are not altogether different from those of his cohort. Many people in my screening were wondering when Billy would start murdering his classmates, or some such. My reply is that many 15yo boys think many of the same things as Billy but have the sense not to say them out loud.
Even after listening to Ms. Venditti I am not sure what, if any, point she was trying to make. If it is just a "slice o' life" exercise then she is pretty close to the border of exploitation of the boy's disability, and I can't tell which side of that border she's landed on.
Just my view.
Dan