Traumatic Brain Injury (TBI) is the most common cause of death and long-term disability in children. Much of the long-term disability stems from neurocognitive impairments that are not greatly helped by current cognitive training and pharmacological treatments for TBI related cognitive impairments. This study tests the hypothesis that a drug, D-cycloserine (DCS), will significantly enhance the effect of cognitive training in correcting cognitive impairments in children with moderate/severe TBIs.