Related studies have found that online courses can make teenagers have more symptoms of depression, anxiety and loneliness (Branquinho et al., 2020).

At present, the response of the whole society to the epidemic has gradually changed. When students go back to school or try mixed (online and offline) classes, adults can't ignore the long shadow left by the three-year online class experience, especially the shaping of their learning, lifestyle and even thinking mode.

Melancholy youth: too far from campus and too close to parents.

The symptoms of depression, anxiety and loneliness may be due to the lack of real group learning environment, that is, "lack of learning atmosphere". In the process of online class, students are no longer faced with real classmates and teachers, and also lack the "sense of ceremony" composed of "hardware" such as classrooms, seats and blackboards. Whether playing games, chatting or having classes after class, students are faced with the same computer and the same furniture. Students can't make eye contact with teachers and classmates in time when they encounter knowledge points they don't understand. If they want to know the answer to the question, they can only turn on the microphone to make a speech or type a question on the public screen for everyone to "pay tribute". Some students may worry that their questions are "low-level", causing everyone to laugh and choose not to ask questions. After all, teenagers are very sensitive at heart.

The influence of online classes on teenagers' learning will also affect their mental health.

First, the development of self-control lacks sufficient external guidance and supervision. According to the author's own feelings about online teaching and the information collected from teachers and friends at home and abroad, we find that the general concern is that young students can't get proper supervision.

In the past three years, the most I can hear from teachers is: "I'm not sure what the students are actually doing in the online classroom." With the change of learning environment and learning atmosphere, many young students with weak self-control seem to be hanging up classes, but in fact they are doing other things.

Teachers often encounter such a situation: students are named to answer questions, but they don't get a response. Perhaps they are well aware of the truth that "even in online classes, they should listen carefully", but their physical and mental development is not yet mature, and they have not developed a perfect willpower. They can choose self-control between heavy homework and attractive entertainment.

On the other hand, an important feature of adolescence is that you can't look at yourself completely objectively. In other words, they often think they have reached a certain level, but in fact they may not. For example, in the face of schoolwork, they always overestimate their mastery of certain knowledge.

Every time the teacher asks my students "What do you think of their basic knowledge" at the beginning of the class, nine out of ten students will tell me "not bad", but in the subsequent study, they will gradually find that their knowledge is actually full of loopholes.

Driven by this mentality of self-misjudgment, it is easy for students to slack off in the next online class and feel that "I have learned it anyway, and there is no problem if I don't listen carefully." Teachers don't know what students are doing behind the screen, and it is difficult to make substantive supervision and punishment measures.

Some foreign colleagues even complained that despite repeated urging, students still insisted on not handing in their homework. At the same time, under the online class mode, teachers usually can't give students positive feedback in time and can't communicate their feelings face to face. When students can't get a positive response from teachers no matter what they do, slack will follow, and self-control ability can't be actively and continuously cultivated.

Secondly, online classroom increases the duration and frequency of contact between teenagers and family members, and the frequency of conflicts and differences between teenagers and family members also increases. Especially when parents can't go out to work for the time being, parents and children are together for almost 24 hours, which invisibly increases parents' concern for teenagers at home.

Teenagers are "rebellious" and eager to get rid of the shackles of their parents. They will feel that their parents are annoyed, always appear in front of them and have no freedom. Even a glass of water sent in by parents out of concern will make them feel that their parents are watching them and don't trust them.

Parents can't help feeling wronged, thinking that everything they do is for the good of their children, accusing the children of failing their parents' kindness in general, starting to increase the frequency of preaching, and finally evolving into more intense quarrels, deepening the rift of parent-child relationship.