Even if there is no national regulation, it is against professional ethics and workplace rules. Take a similar example: I am a designer, and the company received an order, but I privately asked the customer to give me some materials to do privately. Do you think it's okay? I also use my skills to earn extra money!
In fact, if I do this, firstly, the customer will not agree-I have already paid your company, so why do I have to pay you extra? But my company will disagree-aren't you snooping around the corner of the company? Which company can tolerate you doing this?
The reason why teachers can do this is nothing more than to grasp the parents' fear that teachers will work hard on their children. Moreover, even if they report and transfer the teachers, parents have no idea about the level of the new teachers, not to mention that changing teachers frequently is not good for their children, and parents can only hold their noses and admit it. In my opinion, this is not much different from kidnapping.
All the noise in the world is for profit. Everyone has the right to get more benefits, but I hope to have some rules and conscience when making money. For example, some teachers resolutely refuse to accept students from their own classes, and some teachers only use the winter and summer vacations to work in training institutions ... but when you take advantage of the opportunity of teaching, invite students from your own class to attend your training courses, which is just like working in a company, you can spy on the company.