A couple months ago, I did a course on smooth infinitesimal analysis with high school students, based on this post. It is of course tricky to do logic stuff with school students, since they typically have no background in writing and understanding (informal, but reasonably precise) proofs. Still, they liked it, were able to work with infinitesimals, and definitely got the main points.
Here are the notes (in German only, I’m sorry).

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