Mercaptopurine 75 mg/m2 PO daily for 7 days, Days 1-7. Methotrexate 40 mg/m2 IV or intramuscularly (IM) Day 1. Cyclophosphamide 300 mg/m2 IV, Day 1. Cytarabine 300 mg/m2 IV, Day 1. Dexamethasone 12 mg/m2 (std/high risk) or 8 mg/m2 (low risk) PO daily (divided t.i.d.) for 5 days, Day 1-5 (between week 21 and week 68).Decrease dexamethasone to 6 mg/m2 PO daily (divided t.i.d.) x 5 days,Day 1-5 between week 69 and week 101 for all risk groups.