 Rapid early responders will undergo interim maintenance two times and reinduction for one time. Slow early responders will undergo two times of interim maintenance treatment with high dose intravenous methotrexate. For SER, adriamycin was previously administered only when absolute neutrophil count and platelet was normal, but it will be administered without restriction in this study. Both groups RER and SER will undergo maintenance chemotherapy thereafter, with the treatment duration of 3 years from the 1st interim maintenance for boys and 2 years for girls. 