Well, I got the release / debut date of the Science Fair trainer wrong... in my first video, I stated that this machine was released in 1976 (!), and that it hence started the whole business of microcontroller-powered educational computer systems for kids and juveniles.

Turns out I was wrong - a few days after my first video about the Science Fair was released, I got an email from Jason J., a long-time Science Fair trainer enthusiast, who pointed me to the debut of the trainer in the 1985 Radio Shack catalog: 

https://web.archive.org/web/2013/http://www.radioshackcatalogs.com/html/1985/h155.html

He also mentioned the Japanese 1981 Gakken FX R-165 and later re-release as the Gakken GMC-4. Whereas I knew about the Gakken computers, I thought that it actually was the other way around - that the Gakken's were re-implementations of the Science Fair trainer from 1976. Turns out it was the other way around - the Science Fair is a watered-down Gakken FX R-165 with omitted GPIO capabilities. So no real electronics experiments are possible with the Science Fair, unlike the Gakken FX R-165.

That actually makes the Busch Microtronic as well as the Gakken FX R-165 the first such systems of their kind, not the Science Fair as I previously thought.

Thanks to Jason J. for pointing this out! I had found the 1976 date on the web, but obviously, this website is in error as well. Maybe this person mistook the TMS 1000 release year for the trainer's debut year.