Just an additional question/thought…
Are any kids getting As in any courses? Although you say some teachers refuse to give 100s, do they give out As? Generally an A encompasses grades ranging from a 92/93 to 100%. Some schools consider anything over a 96.8% as an A+. (Some teachers will never give A+s even to students with 99% averages: simply against personal or school policy). Of course some of your teachers may refuse to give A grades but then there has to be a top grade in such a class.
Lastly, some schools give out Bs as the top grade for “getting everything correct” or "meeting all of the teacher’s expectations. A grades are reserved for students whose work is beyond correct or fine…As are reserved for truly exceptional work