Place the wide lumbar belt around the child's lower torso first, so it sits as the anchor of the corrector. Then bring the figure-of-8 shoulder straps over the shoulders and adjust them so they gently draw the shoulders back without straining the neck or armpits.
The adjustment should be gentle. Tighten the straps only until you feel light tension; the child should be able to move, twist and breathe normally while wearing it. A useful check is that the belt stays in place and the straps do not dig in, slide off the shoulders, or force a rigid position. The corrector is designed for measured positioning with some flexibility, not hard immobilization.
It can be worn directly on the body or over light clothing — choose whichever is more comfortable for the child. After putting it on, ask the child to sit and move a little, and check whether the corrector stays put. If there is pain, skin irritation or a feeling of breathing restriction, remove it immediately and have the fit reviewed by a specialist before using it again.