 ARM I: Patients receive vincristine sulfate IV on days 1, 29, and 57; dexamethasone PO BID on days 1-5, 29-33, and 57-61; mercaptopurine PO QD on days 1-84; methotrexate PO on days 8, 15, 22, 29, 36, 43, 50, 57, 64, 71, and 78; and methotrexate IT on day 1. Treatment repeats every 84 days until the total duration of study treatment is 2 years from the start of interim maintenance therapy approximately week 119 for girls with T-ALL and 3 years from the start of interim maintenance therapy approximately week 171 for boys with T-ALL. 