For the correction of Juvenile and Adolescent idiopathic scoliosis, companies offer and surgeons use varying rod sizes not based on scientific evidence, but because of personal preference, availability and company loyalty. To date there has been no literature evaluating the benefit or harm of one rod size versus the other. Our dual-arm prospective study will evaluate the amount of radiographic correction obtained using the 5.5mm versus the 6.35mm stainless steel instrumentation rods. These are both standard rods used in the community for this particular procedure, thus no additional risk exists for the patient. The results of this study will help guide surgeons in their decision making process when faced with the multitude of options offered by implant manufactures.