MAINTENANCE COURSES 1-4: (weeks 36-67) Patients receive high-dose methotrexate IV continuously over 24 hours on day 1; leucovorin calcium PO or IV every 6 hours for 3 doses on days 2-3; methotrexate, hydrocortisone, and cytarabine IT and vincristine IV on days 1 and 29; prednisone PO or IV BID on days 1-5 and 29-33; mercaptopurine PO on days 8-28; methotrexate PO on days 8, 15, and 22; etoposide IV over 1 hour and cyclophosphamide IV over 1 hour on days 29-33; and dasatinib PO on days 1-14 and 29-42 OR on days 1-56. Patients also receive G-CSF SC or IV QD beginning on day 34 and continuing until blood counts recover. Courses repeat every 56 days. After completion of maintenance courses 1-4, patients proceed to maintenance course 5.