And found it easy. (Okay, didn't quite get related rates for a while, but when I came back to them I thought, "Oh, where was the problem?"

Mostly because my college algebra teacher was great and made sure we under functions and limits and how to "see" most common kinds of equations.

Had to help some students last fall with their calculus and explained that the capital Greek S (sigma) "sum" symbol is good for a countable number of elements and usually uses a Greek "d" (delta), the long S is a sum as the size of the elements approaches zero and are "infinitesimals". I teach high school science.

Years ago there was a Japanese program in which they taught calculus to 6th graders. I find that students suck at calculus when they ignore the math and think of it as (just) a series of tricks and techniques.