MAINTENANCE COURSES 6-12: (weeks 76-131) Patients receive vincristine IV on days 1 and 29; prednisone PO or IV BID on days 1-5 and 29-33; mercaptopurine PO on days 1-56; methotrexate PO on days 1, 8, 15, 22, 29, 36, 43, and 50; and dasatinib PO on days 1-14 and 29-42 OR on days 1-56.