Kind of a fun coincidence that you are asking about this since I was just thinking about this the other day. I was actually just casually contemplating possible projects and the idea popped into my head.
As a child we used to have two games called "Math Dodger!" and "Spell Dodger!" on Macintoshes at school. Probably not as much fun or as popular as the Oregon Trail but still pretty good within the context of hey-we-get-to-play-a-video-game-at-school. Actually ended up with a copy of each at home too (I actually have the disks but they're 800K so you need a real vintage Mac to read them) and I know I played it some outside of school so it must have been decent at some level, right?
http://macintoshgarden.org/games/...
I guess the game was fun because it really kind of separated the learning part from the game part. It was kind of a simple climb-the-ladders platformer on a single screen where you were this little blue droplet guy and had to run around avoiding enemies and collecting these coin or token things. Each time you reached one you had to answer a math problem or spell a word (depending on the game version) and things obviously got harder based on age settings and simple progression. If you failed the question I think you lost a life same as getting hit by an enemy. There was also a bonus stage where the tokens rained from the ceiling but I don't think this part had anything educational.
If you removed the education component from the main game then it would be a rather simple (maybe mediocre) little game but it had lots of level variations and I think adding in the quick problem solving actually gave it another dimension. The losing a life for getting the question wrong really helped to kind of gamify the education part and maybe drew you in some more. I must have enjoyed it somewhat since here I am writing several paragraphs about it.
I actually wrote about 90% of a engine clone running on MS-DOS back when I was in college. My mother was working as a teacher at the time and wanted some educational games that would run on the ancient PCs they had in the back of their classroom. Never actually completed anything though.
Anyway, I was recently thinking about this when thinking about homebrew and thought that it could probably be adapted to the NES. Certainly the game mechanics and the board layouts are probably very reasonable within the capabilities of the NES. Trying to enter solutions for simple Math problems (all the way from simple counting up to Algebra I, as I recall) would probably work okay with an on-screen keypad type interface but certainly not as good as the keyboard on my old Macintosh. Spelling could work too but on-screen keyboard would be even more clunky than the keypad.
I kind of dismissed the thought after thinking about how the problem solving screen wouldn't adapt as well without the keyboard. After talking through it though doesn't seem as bad. Maybe I should take up this project?
I think the games had just a big cache of pre-built screens but I was wondering if maybe I could generate the different screens procedurally. I'm guessing there wouldn't be a whole lot of interest in this though...
Cheers!