The Movin' Sit & Movin' Sit Jr. are inflatable dynamic air cushions which activates intrinsic trunk muscles to support the spine. The wedge shape encourages a seated posture with a forward pelvic position and the movement makes the user feel off balance if not sitting correctly. The child size version the Movin' Sit Jr. is 10" X 10" and fits perfectly in elementary school desks and other chairs. The Movin' Sit Original is desiged for larger children or floor use and measures 14" X 14". This inflatable wedge seat encourages static anatomical seating while mimicking the dynamic seating motion of a therapy ball. It is great for kids with poor posture and those who have trouble sitting still. In particular, kids with ADHD and/or Sensory Integration Dysfunction will benefit from the Movin' Sit Jr. It can also be used upright in any chair as a back support or on the floor. Adjust inflation to comfort level. Low inventory, buy this great product soon!!!!