You can collect the problems he often makes and find some similar problems to practice. Many search softwares are available now. Set some small rewards, and don't have too many topics at the beginning, so as not to bore the children. It is important to tell children that although there are not many questions, they must answer correctly in order to get a reward.
When the child can meet the requirements, slowly increase the number of questions and limit the completion time. When good study habits are developed, I believe that children's grades will be improved.
Educate children about matters needing attention
Educating children should start with a comprehensive education of morality, intelligence, physique and beauty, and don't pay too much attention to grades. In other words, the child's grades are average, so as long as he is virtuous, who will think that he is not an excellent child? Don't always stare at grades, look at a child from many aspects.
Also, pay more attention to children's hobbies. Children should teach students in accordance with their aptitude. Maybe he doesn't love this subject, maybe his interest is something else, and maybe there will be a surprise discovery.