Until 6th grade we were on a completely different system:
N = Not Satisfactory
S = Satisfactory
E = Excellent
O = Outstanding
I can see such a system expanding to middle school with reasonable results.
How is this any different from an A-F metric, or any other similar system?
If a report card is to tell what the student knows, grades are basically useless. If a student gets a C in math, what does that really say other than when you average his scores it landed between 70-79%? What did he do well with? What did he struggle with? Oh and what about those zeros that crushed a final grade, skewing the average. Do those zeros show what he has learned or are we mixing responsibility/accountability with work?
The best thing to do is define the specific standards you are teaching and then score the student
on his work in relation to the standard. Did he meet it, exceed it, fall below it, or fall far below it? Use whatever system you want to convey the score but tie it to standards, not a generalized grade of who knows what, so it actually means something.