It would depend a lot on the child. If the child can manage him/herself without a great deal of supervision, it could work.
I'm speaking of Sudbury, as I don't know other types of democratic schools. A wide range of behavior is respected as long as it does not harm people or property in the school. I'd suggest visiting your nearest democratic school, have them meet your child, and if it sounds agreeable on both sides, try a visiting day/week.
Best wishes on finding the type of education that works best for your child.