My personal schooling life was thrown into an uproar when I changed schools in 7th grade, and my new guidance counselor thought it apparently was not possible for people to be superbly gifted in English, yet average to poor in mathematics skills. He decided that I had heretofore been "lazy", and that it would be no problem to vault me mid-year into the 7th grade gifted math class, which was in the middle of algebra (if I recall correctly, in my old school we had been doing complex equations with numerals-only, and I had been struggling with dividing by improper fractions).
As you might imagine, it was a sad rout, and that was only skipping me a total of, what, two grades' worth of math? I understood nothing. "Solve for x"? What are these letters doing in the middle of my numbers?" My brain literally meshed into gridlock the minute any authority figure looked at me expectantly, and worse 1:1, and said "OK, now solve this problem." My brain was literally frozen. I can't imagine what it would be like if I had had to make up 6 grades' worth of material, on any subject.