What you wrote about the Wikipedia page is not consistent with what I read on the Wikipedia page:
>While working as a marketing director in the early 1960s, Engelmann became interested with how children learn.
>[...]
>In 1964, he left his job in advertising and became a research associate
>[...]
>In 1970, he moved from the University of Illinois to the University of Oregon in Eugene, becoming a Professor in the University's College of Education.[2][3]
He was never a public school teacher, although he may have taught students as a research associate. He was apparently teaching as a hobbyist, including homeschooling.
The kerfuffle about whether he was "actually teaching", however, actually misses the point. While you can, at least in principle, understand the experience of a student by experimenting on students, you will never understand the experience of a teacher by experimenting on students. Whatever method you come up with or promote must ultimately be implemented by real flesh-and-blood humans working under real constraints (including the limits of their own abilities and emotions) with realistic organizational and community dynamics. This is what I interpreted the original complaint about researchers versus engineers as analogized to software development to mean.