> We now observe preparation gaps so severe that instructors must reteach middle-school mathematics while simultaneously teaching the material students need for sciences, engineering, economics, and other quantitatively demanding fields

I was annoyed to not find specifics. I would be surprised if the K12 school board and university STEM professors are in agreement about what middle school mathematics is.

Trig comes to mind as a common stumbling block. I could be forgetting, but I don't recall much of it on the SAT. If I had to pick one area of math where the gap between learning something initially and actually being shown its broader applicability is the longest, it would be that. Like a decade between SOHCAHTOA and diffeq / fourier probably.