There are several reasons why teachers should not discuss a student's grades or behavior outside the classroom.
* It is a breach of privacy. Students have a right to privacy, and their grades and behavior are private information. Sharing this information with anyone other than the student, their parents, or guardians is a breach of their privacy.
* It can be harmful to the student. Discussing a student's grades or behavior outside the classroom can be harmful to the student's self-esteem and motivation. It can also lead to bullying and other forms of harassment.
* It can damage the teacher-student relationship. When a teacher discusses a student's grades or behavior outside the classroom, it can damage the trust and rapport between the teacher and the student. This can make it difficult for the teacher to effectively teach the student.
If you are a teacher, it is important to remember that you have a responsibility to protect your students' privacy. This means never discussing a student's grades or behavior outside the classroom.