What I know about mathematics, from junior high school to senior high school, is almost the omission of any small link, which will directly affect the later study, and there are also reasons why students lack creative independent learning and error correction ability caused by our traditional exam-oriented education.

Let's put it this way: in junior high school, I often got 100 or 0 in math because I was playful. At that time, I thought I was not afraid of anything as long as I put my heart into it, but I was not.

Because the foundation is not good, you will suffer in high school!

In view of this, I suggest whether to talk to the math teacher in her school, because after all, people are the main teachers who are teaching, and they must know your sister's learning better than others. It seems that such counseling should be more direct and effective.