If your child has special needs such as a physical disability, developmental disability or mental disability it is important to find out how much experience the school has with interacting and successfully working with this type of student. Ask if the school is open to having outside professionals in the school should this be required.
Many preschools provide education to a child even those with struggles. If you have a handicapped or otherwise challenged child, preschool can be a great way to bring this out in them. It's a good way for them to feel normal and respected as well.