Benjamin Bloom, an American educational psychologist, classified students' thinking level into six categories (Bloom's classification) in The Classification of Educational Goals: Cognitive Field published by University of Chicago 1956. After I learned about this classification through teacher Zhang Baoyou's TED talk "Mathematics Makes a High Mind", I found it very valuable. In the speech, Mr. Zhang thinks that most of the teaching in the school is concentrated in the lower three levels:

First, memorization: the memory of specific facts. For example, remember the multiplication table of 1999;

Second, understanding: grasp the meaning of knowledge materials, sort out the facts, and find out the meaning of things. For example, understand the meaning of the equation 1+ 1=2;

Application: the application of information and rules to solve problems or understand the nature of things. For example: be able to solve problems with mastered formulas;