I am not sure where you went to school, but in the New York City public school system, report card grades followed a formula of roughly the following:

  65% exam scores / written essays
  25% homework
  10% classwork

A 65 was basically a D-, and anything less was an F. In other words, a student who receives perfect scores on all exams or written essays (depending on the subject) could receive a D-, as though they had only the most minimal understanding of the subject matter.

So while the report card is meaningless, it is meaningless for a different reason than you suggest. It is meaningless because it has nothing to do with aptitude or education and everything to do with obedience.

These are orthogonal issues and thus can both effect the value of a report card. Beyond that, I agree with your point.

Although you don't mention it, I feel that this post strongly implies that the teachers can't be trusted to exercise professional judgement. What's the point of even requiring teachers to meet standards if you believe that they can't properly evaluate their students?

That's orthogonal to my point. Teacher quality or competence in assessing quality, doesn't have anything to do with whether they assign grades in the ways I've enumerated. I've had absolutely amazing teachers that have graded in those three ways.

Even if they're good judges of quality, it's still a matter of how they determine your grade. Is it good quality relative to what they think your skills are? Is it good quality relative to the rest of the class? Is it good quality relative to what they believe constitutes mastery of the subject? And some teachers curve and some don't.

And I haven't said whether I think teachers should be required to meet standards. I don't even know if it's possible to create good standards.