The investigators objective is to derive and validate a clinical prediction rule for the development of PCS in children and adolescents presenting to the emergency department (ED) following acute head injury. The investigators have three aims: (1) determine PCS incidence at one-month follow-up in children aged 5-17 who sustain a concussion; (2) derive a rule to predict PCS from variables present in the history and physical examination; and, (3) assess the accuracy, reliability and acceptability of the prediction rule in a subsequent cohort. Using a prospective, multicentre study at nine large Canadian pediatric EDs, the investigators will recruit the largest prospective epidemiological cohort of children with concussions in the literature.