Chapter 14 ~ Grading

I read the chapter on grading. I am struggling with how grading the advanced learners are fair. I know we want to try and challenge them and try to get them to “reach high” but I don’t think that they should receive a lower grade in order to push them to do better. I also don’t know what I would do in order to challenge these students. I am struggling with this in my placement now, we have a student whose mother wants to pull her from our inclusion class because she thinks the students are hindering her and not challenging her. I know for a fact that this mother would have a cow if I sent home a project with this student and when I graded it she received a C because even though she met the requirements she could have done better but a lower student received an A because they did better then we thought. How can I challenge some students to do better while the others just need to work hard to catch up to the rest?