The answer to that question depends on the nature and severity of your child's disability. Each child is different, so each child's situation will require an independent evaluation. As the parent, you are the natural guardian of your child until he or she reaches the age of eighteen. As the natural guardian, you have the right to make medical, housing, and other decisions for your child. But when your child turns eighteen, thus reaching the age of majority, those rights are transferred to your child.
If you need to retain decision-making authority, you will have to get it from a court order. A child with a disability severe enough to cause total incapacity, will need a full guardianship, under which all decision-making rights will be removed from the child and given to you. You will have to hire a guardianship attorney who can guide you through the process in your local probate court. Once you are appointed guardian, you will once again have full authority over your child and will be able to make all decisions on his or her behalf.
On the other hand, if your child has a partial incapacity, then full guardianship is probably not necessary. The court can order a partial or limited guardianship. If this happens, you will only have decision-making authority in those areas where your child's disability limits his or her ability to function. Other decision-making authority will remain with your child.
Sometimes, when there is a partial incapacity, a partial or limited guardianship is not necessary. Options, called alternatives to guardianship, may be available and must be used if they will avoid the need for a guardianship. Putting one or more of these alternatives in place will allow your child to retain all of his or her rights while giving you the authority to help and provide needed support.
When should you find out if guardianship is right for your child? Often times special education teachers will urge parents to do so prior to the child's eighteenth birthday. I agree that you should consult with a guardianship attorney at that time so that she can help guide you to a decision that will be in the best interest of your child. If guardianship is necessary, the process can be started within six months of your child's birthday, but the court order will not take effect until he or she turns eighteen.