 ARM IV: Patients receive vincristine sulfate, dexamethasone, mercaptopurine, methotrexate PO, methotrexate IT, and nelarabine as in arm II. Patients then receive treatment without nelarabine as follows: vincristine sulfate, dexamethasone, mercaptopurine, methotrexate PO, and methotrexate IT as in arm II. Treatment without nelarabine repeats every 84 days until the total duration of study treatment is 2 years from the start of interim maintenance therapy approximately week 121 for girls with T-ALL and 3 years from the start of interim maintenance therapy approximately week 173 for boys with T-ALL. 