Generally speaking, American education can be divided into four progressive stages: preschool education, primary education, secondary education (junior high school and senior high school) and higher education.

The first three stages belong to pre-university education, including nurseries, kindergartens, primary schools, junior high schools and senior high schools. Pre-university education is also called basic education, that is, K- 12 education stage (also called compulsory education).

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In the United States, tens of thousands of schools adopt this curriculum system for teaching, covering language arts, mathematics, history, science, art and so on. At each stage, we should set learning goals that are in line with students' psychological development, so as to improve language ability scientifically and effectively and enrich knowledge reserves. In the K- 12 education system, critical thinking ability is particularly important.

Introducing the original K- 12 education system in the United States into general practitioners in North China aims at cultivating students' most lacking critical thinking. When teaching knowledge, they emphasize their own exploration and design experiments, and pay attention to the development process of students' thinking, rather than simply instilling knowledge theory.