When I went to school it was pretty much as TC posted, starting at 64 for D. I have no idea why we did it that way and that was back in the early 90's. It was only for high school though, elementary was O, S, and U and middle school was the standard 60, 70, etc.
It made it pretty difficult to get an A when you had to get 94. An 89 wan't even a B+, it was just an average B.
I did not go to a high achieving school. I went to a rural school in the US where 68 out of over 130 kids actually graduated from HS. Not all of the others were drop outs, quite a few went to technical school. My school didn't offer many electives and only had 2 languages. So, I don't think there is any logic to the decision some schools seem to make to switch to non-standard grading like this.
