[wyantb]

Some games solve this by having different modes of play. "Highscore Mode", "Campaign Mode (Easy/Medium/Hard/etc)". If you did, for example, have a dynamic scaling system, you could have that in some kind of alternate play mode that lets the user just practice, vs. a separate/more static mode that allows eligibility for highscores.

[pjbrunet]

I think the dynamic scaling (difficulty multiplier?) could just be the levels advancing faster like somebody else said. If you solve a level too fast you could get a "wormhole" advancement that just gives you points automatically for the levels you skipped over.

I think this is awesome, not just as a typing tutor but as a spelling tutor. I think adding phrases and word combinations would help teach grammar too. You could also do a synonyms level, an antonyms level (I think even adults would like these) then verb levels, adjective levels, etc.

Here's another idea. A convoy of words come at you (as a sentence) with the verb out in front and you have to shoot the verb first.

Or, totally different game, fly/shoot your way through isometric Zaxxon-like "sentence diagram" landscapes.

PS: This is how I learned my times tables back in the 80s, very similar game on the TI99 ;-)