Traumatic Brain Injury (TBI) is the leading cause of acquired long term disability among children and young adults. Deficits in attention and memory are common and persist for years after moderate or severe TBI. The similarity between these symptoms and those of children with AD/HD, the efficacy of methylphenidate in the treatment of AD/HD, and the efficacy of methylphenidate in improving recovery of animals with brain injuries, support the need to study methylphenidate effects in children with TBI. This investigation of methylphenidate in children with moderate to severe TBI aims to: (1) Assess the acute effects of 2 different dosages of methylphenidate on attention and reaction time when the medication is administered to children early in recovery; (2) Assess the ability of 8 weeks of methylphenidate to improve the rate of recovery of cognitive, memory, and attentional skills in children with TBI; (3) Identify the frequency of common methylphenidate side effects in children with TBI.