CONSOLIDATION (WEEKS 13-19): Patients receive high-dose methotrexate IV continuously over 24 hours on days 1 and 8; leucovorin calcium IV every 6 hours beginning 42 hours after start of high-dose methotrexate and continuing until methotrexate level is < 0.1 uM; triple IT chemotherapy comprising methotrexate, cytarabine, and hydrocortisone on day 1; etoposide IV over 2 hours on days 15-19; cyclophosphamide IV over 30 minutes on days 15-19; high-dose cytarabine IV over 3 hours every 12 hours on days 29 and 30; pegaspargase or asparaginase IM on day 30; and filgrastim IV or SC beginning on day 20 and day 31 and continuing until blood counts recover.