Why recruit non-supernumerary teachers?

In recent years, more and more migrant workers have flooded into cities, and the birth policy has also changed, and the second child policy has been opened. Many city schools are facing great pressure from teachers. In order to solve this problem, the school hired a large number of non-staff teachers. However, the treatment and protection of teachers in the establishment is much better than that of non-establishment teachers, so we should try our best to join the establishment and work more stably.