We had tried (and failed) to make DS school change its grading scale from 6-point (94 is the lowest A-) to a 10-point scale (90 is the lowest A-). Since all HS in the metro area (Public as well as private) had all started to use the 10-point scale.
An interesting thought experiment would be to test, whether teachers using the 6-point scale grade more leniently than those in 10-point scale: ie a 93 in DS’ school is actually a 89 in many other school? I somehow don’t believe so, (why would most schools are using 10-point scale?) but who knows.