Who invented the grading system (A B C D F) that they use in schools and where did it originate? Also: Why, usually, are no other letters used? Are there any books on it?
Man, I’m still racking my brains on this searching google. 
Not that this answers the OP in any way, but I was visiting my 80 year old grandmother a couple of weeks ago and she said that when she was a kid, there were no "F"s; kids who flunked got "E"s instead.
We had that in my school district. The lowest grade was E, not F. Anything below 60 percent was considered failing, though it was designated “E,” not “F.”
When I was in elementary school, E was the highest grade you could get! It stood for “Excellent.” There was also an S for “Satisfactory” and a U for “Unsatisfactory.”
In my elementary school also we got E, S, or U - and we also got effort grades (numerical, I think), which makes me think it’s a touchy-feely educational development. This was in the early 80’s, for what it’s worth. After that, of course, we went to A B C D F.
all the schools I went to had the A B C D F grade scale… but non-primary subjects (gym, art, etc.) had that E (excellent) S (satisfactory) U (unsatisfactory) scale.
So have I stumped everyone on this?
Just to add more barely-relevant data:
My mother, who is in her 60’s and has been a teacher for many years said the same thing as remisser.
My 91 year old grandmother said that they used A, B C, D, F (i.e. not E).
I’m looking at my great-grandmother’s Teacher’s License from 1895, and it only shows number grades. I’ll quote part of the “Explanations” section:
So, at least on this, there is not indication of letter grades. Take that for whatever it’s worth.
Just three WAGs, without any knowledge on where it actually came from:
Either the F is supposed to stand for “failed” or something (but why did they choose to keep the alphabetical scheme for the better grades?), or at some schools there used to be six grades, A to F, and the two worst ones were merged into one (reminds me of the German rail where there used to be three classes; one day, long ago, class two was abolished and class three re-named into two, so there’s now First and Second Class), or the gap between the second worst and the worst grade is to underpin that F is reallllllly bad.
In Ontario public and high schools, 1970s to early 1980s*, we received overall marks as either A, B, C, D, or E (but not F), or as percentages.
Individual assignments and tests were often marked as two numbers a/b, where b varied all over the map, and wasn’t simply 100 to indicate a percentage. Presumably b was related to the number of markable elements in the assignment or test.
I don’t seem to remember seeing the possibility of F instead of E until I hit unversity.
*I qualify by date because it’s probably changed completely by now.
My high school in Illinois in the mid-1980s gave grades of A, B, C, D, and E.
At Rice University, where I went to college, they gave grades of A, B, C, D, and F. Apparently, though, from the school’s founding in 1912 to at least the 1960s, Rice gave grades of 1, 2, 3, 4, and 5, with a “1” being equivalent to an "A. "
I’ll confirm that at least as late as 1990, my high school in Michigan used the A-B-C-D-E system. Hearing about F’s on television always seemed strange to me – where’s the logic in that?
This wasn’t an inconsistency of a single school – Intermediate school (I guess what you’d call middle school these days? 6-7-8), first high school, then last high school, in two different districts within two different intermediate school districts.
My understanding is that because E was sometimes used to mean failure but also used for excellent, confusion on its meaning was inevitable. So the simplest, smallest and most obvious change was to have F for failure replace E for failure. There was no reason to change any of the other grades.
In New York City, during the '50s and '60s at least, elementary schools used E, S and U, while junior highs and high schools used numerical grades, with a 65 being the boundary between pass and fail. Grades were in increments of five points up to 85, when there was an 88, a 90, and then increments of one after that.
MIT had a scale of 0 to 5, and I recall people saying there used to be an E for 1. iIt had vanished by the time I was there, and the grades were A, B, C, D, F.
And no, we did not get irrational numbers as grades.
I went to two widely-separated high schools in the late 70s, with different grading schemes.
In Montreal, we didn’t get letter grades at all – our final report card showed a number from 1 to 99 for each class. Higher was better, obviously.
In Los Angeles, we got the standard letter grades of A,B,C,D,F. This was in the days before computers automated the report card procedure, so the report cards were handwritten. Interestingly, teachers were instructed to write out the entire word “Fail”, instead of just “F”. It was thought that an “F” could too easily be modified into an “A” or a “B” by a malicious student.
Ed
I’ve been trying to find the origins of the grading system at the library, but no dice. I’m one stop away from asking Cecil. That’d be funny. 
Some late night googling -
From the American Association of School Administrators (there’s a mouthful) site:
http://www.aasa.org/publications/sa/1997_12/pardini.htm
I’d google on this Guskey fellow and his research, but my bed is calling.
On the British GCSE and A-level papers I sat the grades were A B C D E F U.
A-D were acceptable as grades
E was awful
F was a fail
U meant it was unmarkable
(ie the person wrote their name and nothing else, or pages of incomprehensible gibberish).
A friend wrote her entire Latin paper in modern Italian, and got a U. She still got into Cambridge though.
In my former school district near Kansas City, they used a variant of E-S-U.
E - Excellent
S - Satisfactory
M - Mean-level(?) or Mediocre(?)
I - Inferior
F - Fail
The rationale was for each of the letters to stand for something and be meaningful, while preserving the usual five-level system.
The F, of course, had to be recognizable to anyone. But that was often undermined by the fact that one extra stroke could turn any F into an E, far more convincingly than an F can be turned into an A or more easily than an F can be turned into a B.
While I was in high school, they changed it to A, B, C, D, F. Then they introduced various methods for getting a GPA above 4.0…