These are demanding high school courses. Many of the high school teachers, frankly, are uninspiring or simply don't teach well. They are mandated to move ahead, whether or not the class understands the concepts.
However, these grades count. Moreover, your son or daughter needs these skills and concepts for the SAT and ACT college entrance exams. If they don't truly understand the mathematics, it will negatively affect their scores.
Understanding these subjects thoroughly will not only improve their grades, their SAT or ACT scores will be significantly higher as well.