Why do primary school teachers invigilate graduate students?

There are usually teachers in our school who are responsible for invigilation during the postgraduate entrance examination, but there are still some transfers from other schools. Generally speaking, there will be as many teachers as possible in our school. Who is responsible for the invigilation of postgraduate exams and needs to complete their professional knowledge before they can take the exams; Whether it is the postgraduate entrance examination or the college entrance examination, there are two invigilators in the examination room, one in front and the other in the back; Yes, a temporary lottery system is implemented for invigilators. Taking China Ocean University as an example, according to Article 21 of the Implementation Rules for the Management of Postgraduate Entrance Examination of China Ocean University, the test sites must meet the requirements of standardized test sites of national education examinations.