Another noteworthy aspect is that students’ thinking levels were distributed differently according to the types of multiplication problems. Level 4 appeared mostly in solving M1 type, whereas Level 3 did as for M2 type. This result implies that more students have difficulties in understanding various inclusion relationships of part-whole and inferring quantities. Note that constructing composite units and engaging in part-whole reasoning iteratively are regarded as the roots of multiplication (Steffe, 1994). Moreover, M2 type of problems is less frequent than M1 type in mathematics textbooks including Korean ones. Therefore, students need to have an opportunity to deal with many part-whole situations