Possible to reverse adoption of former foster child?

We have a situation with a former foster child of ours that we adopted a little over a year ago. He has been expelled from school for stealing but will be going back on probation but if he commits an infraction of any of the school rules the expulsion will be completed. He is in an out-of-school suspension program that sends him to a special school while he is suspended. We had to call the police the other day because he became violent with me and threatened to take off and live on the streets but first he wanted all his "stuff" and money! He was trying to force his way back in the house which I would not allow due to his state of mind at the time. I had no idea what he would do once inside. His bio mother has managed to get some of her kids back and she would take him back but I'm not sure how that would work as she had neglect charges filed against her concerning him and she voluntarily signed away her rights to him. She has court appointed three visits per year. Our family just is not a suitable match for him and we fear we are causing more harm than good. Is there a way to have the adoption reversed and allow his mother to have custody of him again? I'm truly afraid of him at this point ... but having him placed in juvenile detention under a incorrigible (excuse spelling please) child complaint ... I'm afraid he'd simply bend right into the system and become worse and completely ruin his life.