Listen carefully in class, not to listen to every word, but to understand every word the teacher says; Secondly, no matter what children are, they should do some extracurricular exercises, which are a little higher than what is said in class. If you have a foundation, you can teach yourself first, and then listen to the teacher, which will be easier to understand.
About high marks, it is the accumulation of topics. Some topics are regular, and you can master the rules by doing more. The knowledge points in the textbook are chaotic, so it should be sorted into an easy-to-understand text list.
Finally, what you don't understand must be understood in time (for example, four operations, although I don't know why, it seems that some people just don't understand), otherwise it is difficult to learn mathematics well without knowing where to accumulate.
As a parent, P.S. must pay more attention to children and let them become interested in mathematics as soon as possible! It is difficult to learn well if you resist. To this end, you might as well play some seemingly fun games first, instead of just doing the questions.