As health care in the United States moves from quantity to quality, unwarranted practice variation has become a natural target for those wishing to improve care. Variation in provider practice should arise from personalizing care decisions on the basis of each patient' s condition and personal preferences. ''Unwarranted'' variation refers to variation beyond what would be expected based on patient or population differences 1 ; it is due to non-evidencebased, inappropriate, and/or inefficient health care. Unwarranted variation in pediatrics has been demonstrated since the early 1900s, when Sir Allison Glover 2 compared pediatric tonsillectomy rates in geographically and demographically similar areas of England. He showed a .10-fold variation in rates and concluded, "A study of the geographical distribution [of tonsillectomy] in children discloses no correlation between any other factor, such as overcrowding , poverty, bad housing, or climate. In fact it defies any explanation, save that of variation of medical opinion on the indications." 2 Despite broad dissemination of evidence-based guidelines for asthma management, 3 unwarranted variation persists in care and outcomes for children treated in emergency departments and/or hospitalized for asthma. Studies have demonstrated wide variation in rates of diagnostic testing (eg, complete blood counts), interventions (eg, intravenous [IV] magnesium sulfate), transfer to ICUs, hospital readmissions, length of stay, and costs, even after correction for patient characteristics. 4-7 This variation is largely due to the challenges of integrating guidelines into care, which may take up to 17 years. 8