Grades are supposed to tell a student where she stands. When almost everyone receives a high mark, the signal disappears while the ritual of receiving it continues.
A grade is a comparison in disguise
Students read grades relatively, not absolutely. The number matters mainly because it locates them among peers, which is the information they use to decide what to attempt next.
When the distribution compresses at the top, that location is lost. Most students receive a similar mark, and the mark stops distinguishing careful work from adequate work.
The ritual survives the loss of meaning. Report cards still arrive, families still respond to them, and everyone continues to treat a signal that has quietly stopped carrying content.
The correction arrives late and hard
Standardized tests, college placement exams and first-year courses reintroduce a spread. A student who has never been below the top band meets a genuine distribution for the first time.
The experience is often read as sudden personal failure rather than as a change in measurement. Nothing about her ability moved; the instrument did.
This lands unevenly. Students with family members who have been through it get an explanation at home, while first-generation students are left to interpret the drop alone.
Compressed grades push weight onto other signals
When grades cannot separate applicants, admissions and scholarship processes lean on essays, activities, recommendations and testing.
Each of those is more sensitive to family resources than a grade is. Coaching, travel, editing help and access to adults who write persuasively are unevenly distributed.
So compression does not remove sorting. It moves sorting to criteria that correlate more strongly with household circumstances than the thing it replaced.
Students substitute effort for calibration
Deprived of a standing signal, many students adopt a simple rule: work until exhausted, because there is no other way to know whether enough has been done.
That rule falls heaviest on students already inclined toward perfectionism, and it produces long hours without a corresponding gain in learning.
What restores usable feedback
Detailed comments on specific work restore what a compressed grade cannot carry. A teacher naming which paragraph failed and why gives a student something to calibrate against.
Practice tests taken under real conditions do the same, because the student sees a spread rather than a ceiling and can locate herself honestly within it.
Neither requires changing a school's grading policy, which is usually outside a teacher's control. Both require time, which is the resource such policies rarely add.