Grading students

I have studied and contemplated grading in schools.  I taught the 5th grade and college students preparing to be teachers and experienced teachers earning master's degrees.  

If you give me a grade, a letter from the alphabet from A to F, my parents or the school principal or other authority may ask why I got that grade.  I guess that in most cases, getting a high grade, say A or B, will lead to fewer questions than if I get a D or an F. Sometimes, a researcher or experimenter or investigator gets people who earned high grades to answer what they remember of the subject connected to the grade.  If the questions are asked within a year or two of getting the grade, the student can answer them.  But if the questions are asked a decade or two later, the former student may deny having studied that subject or getting that grade.

I imagine I have given something close to ten thousand grades but I can't remember to whom.  I would not be surprised if few of the people graded by me remember the grades I gave them.