Mastery of number conservation by a man with severe cognitive disabilities.

An autistic 21-yr.-old with a mental age of four years was taught number conservation. Mastery of this concept requires concrete operational thought and has not been thought to be possible for persons with severe disabilities. A learning set of 105 problems was used to promote generalization, and a "fade-out" procedure was used to make mastery of the problems as easy as possible. Combination of these techniques produced the first recorded success in teaching number conservation to a person with severe disabilities. This demonstration that one individual can perform at this cognitive level opens the door to research to determine the generality and limits of the potential of other individuals with severe cognitive disabilities.