People who have Autism have difficulties with social interaction, social communication and social imagination, to varying degrees. Every child is difference and can be affected to varying degrees of the above areas.
Asperger’s
This refers to children who have problems within the triad of impairments as mentioned above. The the difference between Autism and Asperger’s is that Asperger’s has not language delays. They should not have a cognitive delay but they may have dyslexia or dyscalculia but reduced intelligence will not be the cause of these problems they also may have difficulties with their fine motor skills.
Pervasive Developmental disorder.
This is used for children who have the same characteristics as autism but not all.