Why can't my 3 yr. old talk?

My mostly normal 3 yr. old has trouble talking.  He tries but most words are only understood by us.  He's been to drs., had his hearing tested, autism screening, but still no answers.  His preschool teacher called me today and said she sees Aspberger's tendencies, lining up toys, playing alone, etc.  He is very social at home, makes great eye contact, loves to snuggle, is very coordinated, and otherwise "normal".  What's wrong?

[Kevin Kennedy, Ph.D.]

He certainly displays a delay in the domain of speech/language and likely requires speech/language therapy to help bolster his development in this area. Relative to the social behavior, many children take time to warm up to the peer social environment, and he will likely improve. If he does not, it does invite the question of whether he might display a condition along the Pervasive Developmental Disorder spectrum. It's a bit early to know, but I'd tend to think more along the lines of slow social development vs PDD.