Honest question:
At what point do the elementary school start assigning grades and percentages? Its been a while since I looked through my old report cards, and my son is only in pre-school, but I seem to recall that report cards were marked based on progress up until a certain point, i.e. no A,B,C,D,F ratings, but instead "Exceptional", "Satisfactory", "Unsatisfactory", "Needs Improvement".
I'm not up on learning theory at the elementary level, so I'm not sure you're supposed to even assign grades at that point.
In my school, it started in kindergarten.