Balance - Seated

Exercise:

Have some one demonstrate sitting in a chair with good posture. Perhaps they are sitting on the edge of the chair so that their knees can lower and their pelvis can tilt to maintain the proper curves of the spine. Or, perhaps they are sitting all the way back in the chair, so that their whole back is supported, also supporting the proper curves in the spine.
The belly stays tucked in.
Have all the students practice this posture.
Sitting on the ground: make sure there is a cushion under the spine so that the pelvis tilts and maintains the proper curves of the spine. Also, in the cross-legged seated posture, tilting the pelvis with a cushion, the knees can be placed on the ground, lower than the pelvis,a nd act as a tripod. this gives further stability. And this posture can be maintained comfortably, and healthy, for long periods of time, once the sitter is used to it.