Is it considered an invasion of privacy for a teacher to read students’ text messages?

From a legal perspective, it is of course an infringement of the right to privacy

The right to privacy means that the peace of private life enjoyed by natural persons and the confidentiality of private information are protected in accordance with the law and are not illegally intruded, known, or collected by others. It is a kind of personality right to use and disclose, and the subject of the right has the right to decide to what extent others can intervene in his or her private life, whether to disclose privacy to others, and the scope and extent of the disclosure.

But in today's Chinese society, people are not surprised by this kind of thing. Of course, few courts will accept it. At most, they will make a coordination. Then you will definitely fall out with the school teacher, which will be very troublesome.

Just pay attention next time.