@JordiGH @goatsarah It's been since the 1990s that I took these classes but I think one of the big difference with DiffEq class was the introduction of partial differential equations instead of the ordinary differential equations we had worked with before. It's possible that the names of classes have changed and "differential equations" today equals "differential calculus" of my days. But even then, and I went to a college prep school, it was only the AP math group that learned calculus. The most everyone else got was "pre-calculus"