Treatment of Patients With Newly Diagnosed Medulloblastoma, Supratentorial Primitive Neuroectodermal Tumor, or Atypical Teratoid Rhabdoid Tumor

SECONDARY OBJECTIVES: * To compare the effects of a computer-based training system specifically targeting language, reading, and learning skills (Fast ForWord, Scientific Learning Corporation) with the current standard of care on reading decoding skills as measured by individual academic testing. * To monitor for treatment failure in the posterior fossa of patients whose tumor bed receives a reduced volume of radiation. * To correlate radiation dosimetry of target and normal tissues with rate and patterns of failure and longitudinal measures of audiometric, endocrine and cognitive effects. EXPLORATORY OBJECTIVES: * To estimate the change in neuropsychological performance from the neuropsychology assessment battery (intellect, academic achievement and cognitive ability) and examine the relationship of these changes to risk group, age at diagnosis, and parent measures. * To evaluate the differences between neurotoxicity in the average-risk patient group with that in the high-risk group through qMRI, and fMRI. * To develop or refine novel models relating impact of medulloblastoma therapy on neurocognitive performance to quantitative and functional neuroimaging measures. OUTLINE: This is a multicenter study. Patients are stratified according to disease risk (high-risk disease vs average-risk disease). Patients in both strata undergo peripheral blood stem cell or bone marrow harvest. * Stratum 1 (high-risk group): * Radiotherapy: Patients undergo craniospinal radiotherapy once daily 5 days a week for 6 weeks. * High-dose chemotherapy and autologous stem cell transplantation (SCT): Six weeks after the completion of radiotherapy, patients receive high-dose chemotherapy comprising vincristine IV followed by cisplatin IV over 6 hours on day -4 and cyclophosphamide IV over 1 hour on days -3 and -2. Patients undergo autologous SCT on day 0. Patients receive filgrastim (G-CSF) subcutaneously beginning on day 1 and continuing until blood counts recover. Patients receive vincristine IV on day 6. High-dose chemotherapy and autologous SCT repeat every 4 weeks for 3 additional courses in the absence of unacceptable toxicity. * Stratum 2 (average-risk group): * Radiotherapy: Patients undergo craniospinal radiotherapy as in stratum 1, but at a lower dose. * High-dose chemotherapy and autologous SCT: Patients receive high-dose chemotherapy, autologous SCT, G-CSF, and post-transplantation vincristine as in stratum 1. Some patients undergo a neuropsychology assessment at baseline, before chemotherapy, and then annually for 5 years. After completion of study therapy, patients are followed every 3 months until month 30 (2.5 years) after diagnosis and then every 6 months until month 72 (6 years) after diagnosis.