I think that children should be taught in classes based on ability level, rather than an arbitrary "grade" system where children are grouped by age.
If a kid's a good reader, he or she should be grouped with readers at or near the same ability. If they're poor at math, the same thing should apply. I think a big problem the system has is of pushing kids on who aren't ready to advance at one thing, which can affect performance in other areas.
Who's with me?