 ARM II: Patients receive vincristine sulfate IV on days 1, 8, 15, and 50; dexamethasone IV or PO BID on days 1-21 for patients 10 years of age OR on days 1-7 and 15-21 for patients 10 years of age; doxorubicin hydrochloride IV over 1-15 minutes on days 1, 8, and 15; pegaspargase IM or IV over 1-2 hours on day 4, 5, OR 6 AND day 50; methotrexate IT on days 1, 36, and 43; nelarabine IV over 60 minutes on days 29-33; cyclophosphamide IV over 30 minutes on day 36; cytarabine IV over 15-30 minutes on days 36-39 and 43-46; and thioguanine PO on days 36-49. 