CONTINUATION TREATMENT: Patients receive methotrexate IV over 2 hours on day 1 and mercaptopurine PO on days 1-7 of weeks 1, 2, 5, and 6; teniposide and cytarabine IV on day 1 of weeks 3 and 7; vincristine sulfate IV on day 1 of week 4; dexamethasone PO TID on days 1-5 of weeks 4 and 8; and vinblastine IV on day 1 of week 8. Treatment repeats every 8 weeks for up to 10 courses in the absence of disease progression or unacceptable toxicity. Patients may also receive triple intrathecal therapy on day 1 of week 1 of all courses and day 1 of week 5 of courses 6-10.