The goal of this study is to evaluate children and adolescents with idiopathic scoliosis who are undergoing spinal fusion using motion analysis, balance, and outcome questionnaires. Little research has been done to evaluate how different fusion levels impact walking patterns, range of motion, posture and balance following spine instrumentation in children with idiopathic scoliosis. Debate still continues whether posterior spinal instrumentation with the last instrumented vertebra at or above Lumbar 3 (L3) will provide sufficient spine correction, greater motion, and better posture and balance when compared to a child with instrumentation at Lumbar 4 (L4). Furthermore, how does the spine fusion endpoint (last instrumented vertebra) impact quality of life, participation, and impairment in children and adolescents with idiopathic scoliosis and how do they compare to healthy age-matched peers. The goal of this study is to compare these two end points using gait analysis, postural stability, and outcome tools with the hopes of providing better clinical care to children with idiopathic scoliosis.