Chalk is used in universities now, but the quality is not necessarily good. I suggest your mother eat more duck blood and pig blood at ordinary times, and tell him not to talk during the lecture, especially when cleaning the blackboard. Stay away from the blackboard after cleaning. This is very effective. I am also a university teacher, so I will pay attention to this aspect. I hope you can communicate with your mother and make her pay more attention.

Your mother should be very happy to have such a filial child as you! ! !