This randomized phase III trial is studying different combination chemotherapy regimens and their side effects and comparing how well they work in treating young patients with newly diagnosed T-cell acute lymphoblastic leukemia or T-cell lymphoblastic lymphoma. Drugs used in chemotherapy work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Giving more than one drug (combination chemotherapy) may kill more cancer cells. It is not yet known which combination chemotherapy regimen is more effective in treating T-cell acute lymphoblastic leukemia or T-cell lymphoblastic lymphoma. After a common induction therapy, patients were risk assigned and eligible for one or both post-induction randomizations: Escalating dose Methotrexate versus High Dose Methotrexate in Interim Maintenance therapy, No Nelarabine versus Nelarabine in Consolidation therapy. T-ALL patients are risk assigned as Low Risk, Intermediate Risk or High Risk. Low Risk patients are not eligible for the Nelarabine randomization, Patients with CNS disease at diagnosis were assgined to receive High Dose Methotrexate, patients who failed induction therapy were assigned to receive Nelarabine and High Dose Methotrexate. T-LLy patients were all assigned to escalating dose Methotrexate and were risk assigned as Standard Risk, High Risk and induction failures. Standard risk patients did not receive nelarabine, High risk T-LLy patients were randomized to No Nelarabine versus Nelarabine, and Induction failures were assigned to receive Nelarabine.