This is a phase I/II study of an investigational drug called ABT-751, produced by Abbott Laboratories, given in combination with chemotherapy drugs used to treat acute lymphoblastic leukemia (ALL) that has come back (recurred). The phase I portion of this study is being done to find the highest dose of ABT-751 that can be given safely in combination with other chemotherapy drugs. A safe dose is one that does not result in unacceptable side effects. After a safe dose for ABT-751 given with chemotherapy has been found, the study will add additional patients to find out if ABT-751 (given at the maximal safe dose) when given with additional chemotherapy is an effective therapy for the treatment of children with relapsed ALL. It is expected that approximately 15-35 children and young adults will take part in this study.