Exceptional describes someone or something that is high above average or someone who needs special educational help because of mental or physical challenges. (adjective)
An example of exceptional is an IQ of 140.
An example of exceptional is a mentally handicapped child who needs a tutor.
See exceptional in Webster's New World College Dictionary
adjective
constituting, or occurring as, an exception; not ordinary or average; esp., much above average in quality, ability, etc.: exceptional talents
☆ needing special attention or presenting a special problem, as in education, because mentally gifted or, esp., because mentally, physically, or emotionally handicapped