UNESCO International Classification of Educational Standards (ISCED) is a universal educational classification system, which is used to describe and compare the educational systems among different countries, regions and educational stages. ISCED divides education into six levels, from preschool education to higher education, and each level has its own specific objectives, contents and methods.

The first level of ISCED is preschool education, which is mainly aimed at children aged 3-5. The goal of this stage is to promote children's physical, intellectual, emotional and social development through games and activities. The second level is primary education, which usually includes 1-6 grades. Its main goal is to provide students with basic knowledge and skills and cultivate their learning interests and habits.

The third level is junior high school education, which usually includes grades 7-9. The main goal is to provide students with more in-depth knowledge and skills and cultivate their critical thinking and problem-solving ability. The fourth level is high school education, which usually includes 10- 12 grade. Its main goal is to provide students with advanced knowledge and skills and prepare them for college or employment.

The fifth level is pre-university education, including secondary vocational education and technical education. The main goal is to provide students with professional knowledge and skills in specific fields. The sixth level is the third level education, including undergraduate education and postgraduate education. The main goal is to provide students with in-depth professional knowledge and research ability.

ISCED not only provides a general educational classification method, but also provides a general language and framework for educational policy makers, researchers and educators, so that they can better understand and compare the educational systems of different countries.