"Very smart children may seem advanced in many ways, but a new study shows they actually lag behind other kids in development of the 'thinking' part of the brain," says Malcom Ritter.

Apparently, the cortex (brain's outer mantle) gets thicker and then thins during childhood and teen years. In comparison, however, the cortex of children who have superior intelligence only reach its thickest stage a few years later.
According to Dr. Judith Rapoport, "the delay may promote higher intelligence because it means a child is older, and processing more complex experiences, while the cortex is building up".

In one of the analysis, kids with the highest IQs only reached maximum thickness at the age of 11 whereas the less intelligent ones reached it at age 9. The children's cortex all thinned out as they matured.

Nothing is set in stone but the findings does show that cortex development IS related to high intelligence. On another note, this study should also help scientists understand what goes wrong in children with brain disorders.