I'm a bit familiar with this only because half my son's team held their kid back before high school. It is pretty common in SoCal… There are state rules regarding high school eligibility that come into play when you hold a student back before high school. In California, the 4 year clock for sports eligibility has starts as soon as 8th grade is completed, so if you repeat 8th grade you could be burning a year of high school athletic eligibility. Many do this but don't get caught, but a super stud that is well known could be found out. There is also documentation you may need to prove that the student was held back for academic or developmental reasons, rather than sports (i.e., you aren't allowed to hold a student back strictly for the benefit of athletics). You should check with you state's interscholastic federation for specific rules that apply.