Although some medical scientists agreed upon the new features discovered and explained by Kanner, others didn't accept his ideas, claiming that autism couldn't be separated from other neurological disorders. Many medical scientists disagreed with Kanner and completely refused to see autism as a distinctive syndrome. This was due to the fact that Kanner failed to clarify various aspects of autism, leaving serious gaps in his research.

By contrast, scientists who accepted Kanner's ideas quickly began to apply his model of diagnosis in their psychiatric practice. However, considering the fact that Kanner's concept of autism was confusing, most medical scientists who adopted his theories applied the model of diagnosis too widely. Due to misinterpretation of Kanner's ideas, more and more people who suffered from neurological disorders were inappropriately diagnosed with autism.

The concept of autism was finally clarified by Rutter in the late 70's. Rutter introduced new terminologies and developed new theories that would adjust the overall interpretation of autism. In an attempt to eliminate the confusion that surrounded the concept of autism, Rutter focused his work on improving Kanner's model of diagnosis. Some of the new criteria introduced by Rutter in the process of diagnosing autism were:

- Onset of the syndrome in early childhood, by the age of 30 months;

- Abnormal social development (regarded separately from intellectual development);

- Slow and impaired development of speech (regarded separately from intellectual development);

- Poor adaptation skills, stereotype behaviors and insistence on routine.

While Kanner claimed that autism and intellectual retardation should be regarded as two separate, distinctive units, Rutter revealed that the concept of autism included some degree of intellectual retardation. Rutter refused to accept that autism should be diagnosed without measuring the levels of performance intelligence and proved that Kanner's syndrome and impaired cognitive functions went hand in hand. While this fact may seem controversial and contradictory to Kanner's findings, the truth is that the Austrian scientist failed to correctly measure the IQ levels of the subjects he studied. In fact, Kanner only discovered good memory and logical skills in his subjects, not accounting for other aspects of performance intelligence. Rutter explained that in spite of their good memory and good logical skills, most autistics present some degree of impaired mental judgment.

Rutter's work had clarified many aspects of autism, enabling medical scientists to diagnose the syndrome in a more precise and approachable manner. Rutter's improved model of diagnosis was a huge step forward in the practice of psychiatry, clarifying certain aspects omitted by his predecessors. Although there are still many uncertain aspects regarding the syndrome identified by Kanner, nowadays medical scientists are able to correctly diagnose children with autism.