A good open class is an important embodiment of a teacher's teaching ability, an important basis for evaluating famous teachers, backbone teachers and academic leaders at all levels, and an important index for post evaluation. Before the open class, the teachers read a lot of materials and even learned the wonderful designs of many famous teachers. In addition, colleagues put forward many constructive suggestions. Therefore, most of them follow the additive thinking, and the teaching design is a master. Because of the lack of subtraction thinking and class washing, they didn't ask the following three questions: what content is unnecessary, what content needs to be slimmed down, what content needs to be integrated, and what content doesn't wash away the surface, show the content and lack the essence.

It is common for the classroom to be loose at the front and tight at the back. The classroom lead is too long, which violates the golden period of classroom learning. Most of the previous questions are relatively simple, which need to be discussed in the self-study meeting, displayed and fed back in the seminar, that is, students will learn simple questions repeatedly at first sight. It seems that time is running out when most students can't solve problems independently and need cooperation and sublimation urgently. In order to ensure the integrity of the classroom, we should quickly turn over the courseware and do it once and for all. In the words of students, it is "it is useless to learn, and it is not a study if you can't learn."