Now, here's two tough ones; both are - I think - puzzle books with a key gimmick. Now I have nieces, I'm curious if they still exist because I think they would take to them.
Regarding the sort of gimmick in question: When I was young, I was very fond of the Questron line - educational books that came with a electronic pen; Answers to questions would be linked to a box; and if you pushed the pen on the box with the correct answer, it'd give a 'win' sound; if not, you'd get a 'lose' sound. There were quite a few things in that range with various complexities of pen (I recall the 'challenger' which had timers and 'lives' as well).
I'm not actually talking about the Questron line directly, but that's the *sort* of product I'm talking about: Educational puzzles and quizzes linked with a device that verifies your answer in some way. I *think* they're books - I know for certain that the first one is - but it's possible that they came in some other (gamey?) format.
The first was an educational quiz book that came with a simple blue plastic frame. There were holes in the frame; with switches you could change the shape of the hole (I *think* circle, square and triangle). You'd go through the quiz setting the shapes that correspond to the correct answer, then line the frame up over a jumble of shapes on the side of the page; looking through the holes, you want to check that the holes in the frame match up with the shapes visible below it.
The second is something I encountered buried in an old UK school storeroom; my gut would place it from the 70's or so. You'd have a tray of sixteen tiles, looking something like a sliding block puzzle. The tiles had numbers on one side, colours on the other. In this, the associated puzzle/quiz book (or maybe cards?) would challenge you to arrange the tiles in the tray in a prescribed way to answer the questions (I think depicted as "The top-left question being "What A is a big red fruit", and answer 5 being an apple, so you'd put tile 5 in the top-left). After answering all of those, you'd close the frame and flip it, and you'd now have an arrangement of colours visible through windows, which you'd compare against the answer key.
If it's any help, for this second one, I've got something
like "Mastermind" in mind for the name of it. I doubt it actually *is* Mastermind, but it might be something along those lines.
I was going to list a third one, too, but I've just remembered it in amongst all the rest: It's Brainy Blocks:
