Evaluate sitting without support at 6-month visit and getting into sitting position at 9-month visit, or until achieved.
A child is not sitting independently by 7 months or getting into a sitting position at 9 months: CK and referral
What does weakness in achieving and maintaining sitting look like?
Sitting without support**: 50% by 5.9 months, 75% by 6.7 months, 90% by 7.5 months
Getting into sitting*: 50% by 8.5 months, 75% by 9.5 months, 90% by 10 months
*Source: Denver II
**Source: WHO Multicentre Growth Reference Study Group: WHO Motor Development Study