Sitting in a Huple, a patented hemisphere-like tool, permanently stimulates the vestibular system, thus improving the balancing ability of children with movement disorders. The Gézengúz Foundation for Children with Birth Injuries has been successfully applying this tool in therapy. By attaching x-Inertial Measurement Unit, a wireless three-dimensional orientation sensor, to the Huple, it can serve as an input peripheral for simple PC games. Children are thus motivated; they willingly perform balance training as well as participate in the game-like test. This improves the accuracy and reproducibility of the assessment. Knowing the actual state of the participants is an important element of feedback for the therapy. This paper describes in detail the development of the therapeutic and assessment method on the basis of the Huple: the definition of the movement pattern, the parameters characterizing the movement, and the algorithms used to rank children. Measurement series of 10 children with movement disorders validate the effectiveness of the game-like assessment.