Intersting in that we got rid of an extra year in HS here a few years ago, it was really rare for kids to go back for an extra year of school. Nowadays, in my sons grad class, close to 30% would repeat for either social and athletic aspects, or improving grades to get into the right school.
I don't think it should be legislated out, most boards would provide an age maximum that would help define eligibility on this basis. There are lots of kids who aren't looking at their athletic prospects solely (even if they are - thats a personal choice entirely), I think the harm done to the majority who are in circumstances that require an extra year outweighs everything. Life is always measured by the journey, not how fast it takes.