I’ve often thought it very unfortunate that we leave calculus so late in K-12 education, and for some students never get there at all (at least in my country). I remember spending most of my childhood mystified about what this mysterious “calculus” thing was, and then finally getting around to learning it and saying “oh, it’s just that?”

And then once students are initiated into the (disappointing) mysteries of calculus, what next? They spend the next few years mechanically carrying out analytic differentiations and integrations of a bunch of ever-more-artificial one-dimensional functions. Do you know what the integral of tanh (x + x^x) is? You shouldn’t, because it doesn’t fricking matter! Most of the actually useful integrals that anyone would ever calculate in real life turn out to be only solvable numerically.

In conclusion, put an introduction to the intuitive ideas behind calculus earlier (Year 7), emphasise numerical over analytic solutions, and use the time saved to move on to things like multivariable calculus (and path integrals, which I still don’t understand properly).