It’s more that the A+- system is supposed to help identify a student on the edge. “You have a B+, which means that with a bit more effort, you could be an A” in comparison to “With a B-, you’re at risk of getting a C”. It also helps create more granular buckets out of a percentage scale, which most teachers seem use on grades behind the scenes.

In Russia we use Excellent, Good, Satisfactory, Unsatisfactory and Weak from 1837. The worst grade wasn't used for some time scools but is coming back in common practice for missing work ([0]English Wiki doesn't have it but states that it's a 5-point grade system).

[0]https://en.wikipedia.org/wiki/Grading_systems_by_country#Rus...

Lithuanian schools in up to about 1998 (might be wrong on exact year) had same system, then it was changed to 10 grades, but the lowest grade - 1 was ever used as a disciplinary action. Lowest you would get for failing assignment or homework was a 2. But even when it was 5 grade system the 3-, 4+ or 5- was quite regular occurrence and depended on teacher and subject mostly, as +/- were not accounted officially so 4- was exactly same as 4 for the final grade of a quarter/trimester.

A few of my teachers who'd used +/- signs added them to differ between a strong qualification of work to the grade and a one step for higher/lower grade respectively, i.e. 3- converts to "almost 2", which is just a written clarification.

I saw once a 2+!