'No one understands how capable they are'

Kelly Hunt got the diagnosis when her son was 3 weeks old, and she cried for the next two months.

Doctors and therapists told her Kevin, who has a sex chromosome disorder, would be severely mentally retarded and never be able to do much of anything. They were wrong.

Kevin is now in school, and earlier this week Ms. Hunt found out the 7-year-old could read even though he has yet to speak. The discovery, which evoked a mixture of surprise and elation, came on a visit to the Crofton office of Dr. Carole Samango-Sprouse. Ms. Hunt and her family traveled all the way from Iowa for the appointment with the neurodevelopmental...