Children in this group were provided with base-10 and unit blocks. Each base 10 block is 1 cm × 1 cm × 10 cm in size. Each unit block is 1 cm × 1 cm × 1 cm in size. The research assistant gave explicit demonstrations of how to use both base-10 block and unit blocks to construct two-digit number. First, the research assistant placed out ten unit-blocks in a line and then put a base-10 block along to the ten unit-blocks. They would tell the students that the two set of blocks were equal numbers of “10”. Next, the research assistant demonstrated the way of constructing number 35, saying: "Can you count how many tens in 35?" They then counted out three 10s and five 1s in such a way like "one ten, two tens, three tens......one, two, three, four,