If you have a poor foundation, be careful in class. Find an excellent student and practice more questions after class. If you are not sure, ask your deskmate.

First of all, I am not used to the new environment and I am not serious about my study.

The second is to listen carefully, but I just don't understand. The third is that the topic is difficult and the whole class generally has low grades.

In fact, the most important thing in high school mathematics is basic knowledge. You can buy him a workbook for him to do. Of course, you can also ask a tutor or go to a cram school. You can also communicate with the teacher, ask the child why he got so low in the exam, and help him learn math with the teacher.