Both my kids were 3-4 weeks early by planned cesarean section. Long story, but it had nothing to do with their development and everything to do with concerns of my uterus holding up. They did everything from day one on track or early. Both of them were kind of scarily aware newborns.
Rather, I think it's that babies who arrive early are more likely (just statistically, again) to have had some problem affecting their development, whether genetic or environmental, that both increases the chance of being born early and decreases expected IQ and development speed.
I buy into this theory.
