It sounds as though your child's mother is unable to control your son. Her decision to let him drop out of school clearly shows that she doesn't have the ability to parent him. You should meet with a Certified Family Law Specialist in your city to discuss how you can get custody of your son and put him on the right track.
In most jurisdictions, the requirement to pay child support for an adult is based on the child's having severe disabilities. Your son's specific disabilities may qualify him for special programs through your state or local government that may help him become a productive, self-supporting member of society. Perhaps your attorney knows of such programs available in your neighborhood.
Your son's mother's decision to move to Florida may not be in his best interests. You should sit down with your son and discuss his thoughts about moving. Many children with disabilities are reluctant to change their environment. It's important to examine the impact of the mother's decision to move to Florida on your son. It's clear that you and his mother don't agree on the issues concerning his education. It's always difficult to co-parent when one parent doesn't value an education.
I wish you the best of luck in this situation.
Steven A. Mindel has been certified as a Family Law Specialist since 1998 and heads the business and transactional department of Los Angeles firm Feinberg, Mindel, Brandt and Kline. He serves as a Judge Pro Tem for the Los Angeles Superior Court, Family Law Division and is the Family Law expert for CouplesCompany.com.