my question basically reduces to how to build from the ground (first to a high-school student
I agree with Justin Skycak about presenting logarithms as an arithmetic operation by analogy. I think a great example of doing this is on a YouTube video posted about a decade ago by Vi Hart called "How I Feel About Logarithms. " Vi Hart goes back to the number line.
way of arriving to e
My view is that an application orientation in every high school math course except geometry (where proof demands rigor) helps high school students learn math for the general public. The usual math pedagogy where I live seems to introduce e as a useful number to high school students in the application context of continuously compounded interest, and then it's revisited later with more rigor in the calculus context. That seems to work ok.
the logarithm procedure and the step from discrete to continuous (in the sense of continuous function).
First, as a pedagogical standpoint, I feel the logarithm is the first moment when one can introduce critically the concept of continuity.First, as a pedagogical standpoint, I feel the logarithm is the first moment when one can introduce critically the concept of continuity.
Uh oh. I wouldn't trust your feelings about this.
The transition from "a formula for discretely compounded interest" to "a formula for continuously compounded interest" might be the first moment that the potential exists to introduce critical thought about continuity. But I wouldn't do it then, and I wouldn't do it when logarithms are first introduced later or when they are discussed again in high school calculus.
I believe discrete versus continuous function concepts are intuitive to most students in real-world contexts long before high school. The connection between logarithms and continuity seems tenuous to me. When something is intuitive-but-not-rigorous-yet to a student like continuity, I wouldn't mess with it by an example of using something else like logarithms.
I'm having trouble being both motivating and rigorous when introducing log values that are not natural.
I agree with Justin Skycak again. It's enough to discuss rational numbers, but don't worry about real numbers in this context in high school.