These tests are not looking (much) at advanced courses like Calculus.

This is more “what percentage 9th graders can read at a basic 9th grade level”, “what percentage of 3rd graders can multiply and do basic 3rd grade math”.

These numbers should be in the 80-90% range. But they are not. And note: the majority who are performing well below grade level are not failing. They are probably getting C’s and getting promoted to the next grade. Meaning every year they fall farther and farther behind.