Simplify the following text for a Grade 12 native English-speaking person.
Original: Within the six disability categories , athletes are divided according to their level of impairment , in a functional classification system which differ from sport to sport .
Simplified: Within the six disability categories the athletes still need to be divided according to their level of impairment . The classification systems differ from sport to sport , and are intended to open up sports to as many athletes as possible , who can participate in fair competitions against athletes with similar levels of ability .