Typically developing infants reach the important sitting milestone at 6-8 months. They have good balance in sitting, are able to reach in all directions and start to move from sitting into the crawling position.
Preterm infants tend to sit a little later, at 8-10 months, even when the corrected age is used.
Infants with coordination difficulties (DCD), those at risk for autism, and infants with global developmental delay, joint hypermobility, low muscle tone and a very cautious nature are often late learning to sit.
Learning to sit independently is a very important milestone: the infant gains a whole new way of seeing the world and the hands are freed up for exploring objects and using gestures to communicate.