Grades Before Sports

A debate that has been around for a while is whether or not a student should be able to participate in sports if they have poor grades.  At the high school and college level students are not allowed to play if their grades are below a C average.  However, there is not a strict policy about elementary school children.  If a young child is not doing well in school, does that mean they can't play sports?  I agree wholeheartedly with the high school and college rule.  I don't necessarily agree with holding an elementary school child out of sports due to grades though.  I think sports at a young age is good for helping with the development of social skills and boosting self-esteem.