Whether your child is just beginning their scholastic journey, or already pretty far along, having a solid learning foundation is key to success.
Most often the student is able to pass a particular lesson, however, they really haven't grasped the concept. While this may get them a passing grade for now, these lessons are vital building blocks that are needed for future lessons.
I find that most students are fully able to cognitively understand these studies if approached in different ways. Let's face it, we do not all learn the same.
Many students that do not understand the lessons may simply be bored with the topic. I try to make learning a fun thing, not just a stuffy "read this then answer these questions" plan.