This study is a multi-phase, multi-site methylphenidate (MPH) trial in childhood cancer survivors. Study participants that meet inclusion and exclusion criteria are screened to ensure that they have adequate global cognitive functioning (IQ > 50) and have academic and attention difficulties that might be managed with MPH. Following the screening phase, qualifying participants take part in a two-day, in-clinic, double-blind, cross-over trial during which they receive MPH (0.6 mg/kg; maximum dose, 20 mg) and placebo (inert substance) in a randomly assigned order. Patients who do not have a significant adverse reaction during the two-day trial go on to participate in a randomized, double-blind, placebo-controlled, three-week home cross-over trial consisting of placebo, low-dose MPH (0.3 mg/kg; maximum dose, 10 mg bid), and moderate-dose MPH (0.6 mg/kg; maximum dose, 20 mg bid). Patients are then selected for participation in a 12-month open-label MPH trial if they show improvement over placebo on a parent and/or teacher rating of attention during the three-week home cross-over trial. The 12-month open-label MPH trial includes individually titrated MPH dosing to maximize clinical benefit, monthly monitoring of side effects and regular acquisition of parent and teacher ratings of attention and behavior. Laboratory measures of intellectual function, attention and memory are conducted at the end of the 12-month trial.