1, the first time: there are specialized schools and full-time teachers in human society. People have shifted the responsibility of educating the younger generation from family to full-time teachers, which has caused great changes in the way of education.

2. The second time: the emergence of human writing system. In the process of learning, people regard writing as an educational tool, which is as important as spoken language and gestures. In addition to word of mouth, teaching has also undergone word training, and educational methods have undergone major changes.

3. The third time: the emergence of printing. After the invention of printing, books can be printed in large quantities, and textbooks have been widely used in education, which has caused a major change in educational methods.

The fourth time: the rapid development of modern science and technology. With the rapid development of modern science and technology and its wide application in the field of education, great changes have taken place in the way of education again. This is what we usually call audio-visual education.