Another example where this analogy stops working is that in school the students usually get the same/comparable assignments, that is somewhat the point of those. As the goto hard-problem-person at my current workplace I am pretty sure that it is absolutely impossible to compare my work to the work of my collegue who just deals with the bread and butter problems, it isn't even the same sport. How would you even start doing a productivity comparison here, especially if you understand 0 about the problem space
A significant percentage of people in an organization create the problems they solve.
Managers suggest that an employee must "go above and beyond" their ordinary duties to get an exceptional rating.
But that just means that "going above and beyond" is, in fact, a duty. The problem is it's an ill-defined duty which is even more susceptible to the whims of what the manager thinks counts as "above and beyond." Good managers give clear rubrics of performance.
To me, "meets expectations" says that the employee's error rate was at acceptable levels and "exceptional" means they had almost no errors whatsoever.
What's interesting is that school grades often doesn't follow a normal distribution, especially for easier classes. I suspect that getting an "A" was possible for 95%+ of students in my gym class and only 5-10% of the students in my organic chemistry class.
In the same way, some jobs are much easier to do well than others.
So we should expect that virtually all administrative positions will have "exceptional" performance, which is to say that they were successful at doing all of the tasks they were asked to do. But for people who's responsibility-set is more consequential, even slightly-above average performance could be 10x more meaningful to the company.