This excerpt shows that the teacher pushed students to use symbols to represent the formula for calculating the
perimeter of a rectangle and a square. In the same lesson, Mr. Liu not only discussed with students the concept of the
perimeter of a circle, but also expressed the perimeter as a formula (C= 2r).
The instructional approach was quite different in the U.S. classrooms. For example, in Mr. M’s second lesson, he
asked his students to recall the circumference of a circle while he spent about 1 min discussing the circumference of a
circle. Below is the excerpt from the instruction.