MAINTENANCE THERAPY** (ALL PATIENTS): Patients receive vincristine IV on days 1, 29, and 57; oral dexamethasone on days 1-5, 29-33, and 57-61; mercaptopurine PO on days 1-84; methotrexate IT on day 29; and methotrexate PO on days 8, 15, 22, 29, 36, 43, 50, 57, 64, 71, and 78. Treatment repeats every 12 weeks for up to 2 years (for female patients) or up to 3 years (for male patients) from the start of interim maintenance I.