My bad; thanks for the FYI.
FWIW, a little parental crowing...my son started failing math in the 4th grade, and after a few teacher conferences we finally realized it was because he was bored to death. Since it was a Lutheran school and the teachers and we went to the same church, I was able to set up a compromise: son promised to do the assignments, and in return I would teach him pre-algebra. Long story short, he finished high school with calculus III, and took the advanced math summer camp for entering freshpersons at Rose-Hulman, by which point he had long left his father behind (my limit, no pun intended, was practical calculus for the MBA). He's in his 30s and a transportation planner in AZ now.
Calculus III is one of the more difficult calculus classes. I passed Differential Equations (Calculus 4) put I knew I reached my limit at least in that field of mathematics. Now linear Algebra was fun and very useful too. Sadly it's been so long ago I've mostly forgotten all I learned. Good job on your son.