 ARM I: Patients receive vincristine sulfate IV and escalating doses of methotrexate IV on days 1, 11, 21, 31, and 41; pegaspargase IM or IV over 1-2 hours on days 2 and 22; and methotrexate IT on days 1 and 31. Patients with DS also receive leucovorin calcium PO 48 and 60 hours after each methotrexate IT dose DS patients excluded as of 092910. 