Regimen A: Once blood counts recover, patients receive high-dose cytarabine IV over 3 hours on days 1 and 2; pegaspargase IM on day 2; low-dose vincristine IV on days 22 and 29; high-dose methotrexate IV on day 22; leucovorin calcium IV or orally beginning 42 hours after start of high-dose methotrexate and continuing every 6 hours for at least 3 doses; oral mercaptopurine once daily on days 23-27; etoposide phosphate IV over ≥ 1 hour and cyclophosphamide IV over 1 hour on day 29; and methotrexate IT* on day 36. Patients also receive G-CSF IV or SC beginning on day 3 and continuing until blood counts recover. Treatment repeats every 42 days for 4 courses (with the exception of IT methotrexate which only repeats for 3 courses).