1. 我正跟女儿做这个.由浅入深.有些问题在challenging的同时又紧扣基本概念,我觉得很不错.: Primary Math Intensive Practice (http://www.singaporemath.com/Primary_Math_Intensive_Practice_U_S_Ed_s/147.htm)
2. 这个是听说的,我还没用过: Math Super Stars: http://it.pinellas.k12.fl.us/schools/curlew-es/studentconnect/mathsuperstars/mathss.html
