The learning objectives should be kept in mind when reviewing a textbook. Parents can think about which learning objectives can be achieved by using the textbook and which will need extra experiences. Parents can find ways to get the extra experiences that might be required. This may mean parents have to work with their children themselves, or encourage the teacher to provide supplemental instruction, or perhaps find a tutor. Whatever might be required, it is up to parents to take the initiative to insure that these needs are satisfied.
Parents can promote learning at home.
Students need to spend sufficient time working on mathematics at home. They need a reasonable work environment and good study skills as well. They may need supplemental materials to study in order to meet their needs. Parents can follow their children's progress carefully. This means more than just looking at the grades that come home from school.