that's why people want it dictated

If you can determine if it's better for the child to remain with their parents or not, then it makes sense to give the decision legal force. The problem is with the determination. How a child will feel in foster care is virtually unknowable until they're in that situation. Will they miss their old family, or will they say 'good riddance'?
It seems to me that this boy was taking the path of least resistance, and found putting up with his old family was better than taking flak for not putting forth effort at school. Just as living with a new family was better than jail. Sudbury-style home-schooling would've been a better choice for him, in my opinion.
This sounds like battered-wife syndrome, and probably would require counseling the minor. However, I could easily see this victimizing the child, just like the child abuse industry does. Giving the child the choice does eliminate some instances where they are being neglected/mistreated, though. Once that's done, the only other thing to do is convince them to leave their family.

An alternate solution is to force the mother into rehab.