It is the exam, and there is usually an experimental class after the exam. If you don't take the extra test, you can't be assigned to the experimental class. In the extra test, you can enter the experimental class if you get good grades. How to be assigned to a science experimental class, a liberal arts experimental class and a foreign language experimental class seems to depend on your grades. The same is true for regular classes, with average placement. There is no so-called poor class, and there is no so-called good class. As for which teacher to teach, it is fairer to draw lots.