Development of sitting: overview

Infants are born with a very rudimentary ability to briefly lift the head when supported in sitting position. Over the course of the next  6-8 months learn to maintain the head erect and extend the trunk when when supported in sitting, then learn to sit with arm support and finally to sit independently, reach in all direction and transition to prone kneeling. 

Theses functional developments are associated increasing ability to integrate information from the vestibular proprioceptive and visual systems that allow the infant to stabilize the trunk and head in space, and anticipate and adapt to perturbations created by moving the head and trunk, and reaching in all directions. 

For TOMT Subscribers:  To view video clips of sitting at each age click on the blue links More about a TOMT subscription

A quick tour of the development of sitting 

The neonate 

In supported sitting the neonate assumes a flexed position of the trunk. He is able to raise the very head briefly when supported around the upper torso. 

sitting-newborn_1.jpeg       M 2w sitting.jpg 

Sitting 4-6 weeks 

By 4-6 weeks the infant has started to develop extension in the upper thoracic spine when supported around the upper torso in sitting. 

When supported around  the chest, the infant  is able to lift the head briefly to look at an interesting object or face. (AIMS sitting sub-scale: sitting with support.)

will 4w sitting 4.jpg   will 4w sitting 3.jpg

When supported around the hips the infant's trunk slowly drops forward. However, the infant is able to maintain a degree of extension in the neck and upper thoracic spine. 

will 6w sitting 1.jpg

10-12 weeks 
At this age the infant is able to hold the head erect and in the midline when supported around the trunk. 

Will 11w sitting 6_0.jpg

When supported around the pelvis, the infant sits with the trunk inclined forwards and is able to maintain this position for longer periods of time before collapsing right forwards. 

Will 10w sitting pelvic support 1_1.jpg   Will 10w sitting pelvic support 2_1.jpg   

The head is extended, there is some upper thoracic extension and  and the scapulae are retracted (Bly Third Month)

Will 11w sitting 2_1.jpg    Will 12w sitting thracic extension_1.jpg

4-5 months

At this age infants start to prop themselves on their arms and can maintain this position briefly, before losing their balance and flexing forwards. (AIMS Sitting subscale: sitting with propped arms.) 

L 6m prop sitting.jpg

When sitting on a lap and firmly supported around the hips, 4-5 months infants will actively reach for toys. At this age the infant is usually more focused on reaching a toy than on maintaining balance. 

Sitting on my lap 7.jpg   Sitting on my lap 3.jpg

5-8 months: sitting without arm support

Sometime between the ages of 5-8 months infants learn to sit  briefly without support. (AIMS sitting subscale: unsustained sitting without arm support it.)

However balance is poor and the infant is not able to reach for toys or turn head. 

R 8m sitting 11.jpg

The newly sitting Infant is usually able to stabilize the trunk and maintain balance when provided with firm support around the hips and thighs.

L 8m sitting.jpg

Sitting without support (7-9 months)

By the age of 9 months most infants are able to sit erect with the shoulders aligned over the hips. (AIMS sitting subscale: sitting without arm support 1)

Balance is good and the infant is able move look around and reach for and manipulate toys. 

W 8m sitting 1.jpg     will 7m2w sitting reach side 18.jpg

Active sitting 8-10 months

At this age the infant is very active in sitting, reaching backwards, across the body, moving into and out kneeling. 

W 8m sit 2_1.jpg

7-9 months: infant rotates trunk to reach back for toys 
​(AIMS sitting subscale: reach with rotation in sitting)

W7m2w sitting 13.jpg


8-11 month: moves from sitting to prone kneeling
(Aims sitting subscale: sitting to four point kneeling)

W 8m sit to kneel.jpg

Read more 

TOMT 0-3 Training Sitting Guide

For TOMT 0-3 subscribers
Development of sitting 

Assessment of sitting: from sitting with support to active independent sitting

Activities for training sitting 

More about a TOMT subscription