Not illegal. However, it may violate the regulations of the local education bureau, which may be illegal but not illegal. If you are an on-the-job teacher at school, it is illegal for teachers in most areas to tutor. Teachers do their job well and occasionally do private education. As long as no one reports it, there is generally no problem. If you don't attend classes, you just want to earn extra money, and you will be expelled in serious cases.
In fact, most in-service teachers are private teachers. If you are a freelance teacher, such teachers have a bachelor's degree and a teacher's qualification certificate, and generally work in a training institution or as a tutor. There is nothing illegal about their tutoring, but it violates the policy of double reduction, but now it is actually relaxed.
People have to live, and some special students really need family education, parents, students and teachers to win. If it is an undergraduate tutor, college students usually do homework counseling, and their job is to study. Therefore, tutoring will not spend too much energy, and my own experience is limited. It is nothing more than earning extra money, accumulating experience and social practice.
College students will not even violate the policy of double reduction if they take the place of parents to help with homework. Tutoring is a kind of civil behavior, and there is no relevant provision in our laws. If there is a contract between the tutor's employer and the teacher, it is illegal to violate the contract in private tutoring.
Harm of make-up lessons
As far as school hazards are concerned, paid make-up classes disrupt the normal teaching order. The extra high income brought by paid remedial classes has made a small number of low-quality teachers move their minds and make small calculations. For their own self-interest, they do not hesitate to harm the interests of most students. They don't talk about key and difficult knowledge in class, but they talk about it in their own remedial classes after class, which makes parents and students complain!
As far as social harm is concerned, paid make-up lessons bring bad social atmosphere and cause unfair education. Social educational institutions use high salaries to induce excellent teachers in public schools, seize high-quality educational resources, and then charge high tuition fees, which makes more ordinary families discouraged, artificially creates unfair education and makes the public extremely dissatisfied.