My Dad actually experienced the transition in a really funny way!
He grew up in a little farming community right outside a mid-sized city. They had a three-room elementary school (first and second grade, third and fourth grade, fifth and sixth grade), but then after that they went to middle and high school in the big schools in the city. Except, they had a special experimental program for kids in 5th and 6th grade they had identified as advanced in every school in and around the city, where they bussed them all in to a central place for advanced teaching half a day once a week. And Dad was in this program in like 1965.
Except, there wasn’t really a set curriculum or anything, because it was experimental. They just had a couple of their best teachers do whatever they wanted with the kids. It was nothing like the later “gifted” programs,” it was a lot less pressure and a lot more interesting things. One of the things they learned was plate tectonics, which was not just cutting edge, it was bleeding edge science at the time. So my Dad learns all about plate tectonics and goes home just happy as a clam.
Not much later, he’s getting a geology/geography lesson in his regular 5th grade class, and it’s out of the standard textbook with the standard explanations from the pre-plate tectonics theories.
So my Dad pipes up that actually that’s all wrong, because he learned it in his special class!
And the teacher says, “All right then, if you think you know better, you teach the class.”
My Dad is autistic, though undiagnosed. (In the 60s, extremely few people were getting diagnosed.) He did not notice the social undercurrents.
He said, “sure!” and popped up and took the eraser and erased her diagrams from the chalkboard, took the pointer out of her hand, and taught the class what he’d learned in his special program. While the class was sitting there in shock and fear because they could see how the teacher was seething with rage. But he didn’t notice, he just taught the class and then sat back down.
The teacher sent home a nasty note and had a talk with his parents. But my grandparents were not sympathetic, because after all, it was her own fault. If she didn’t like what my Dad did, she shouldn’t have made the offer for him to teach.