I had this idea while taking the Grammar Course Challenge. Instead of having the objective of the problem: "Choose the preposition that makes the most sense in this sentence." and then having multiple choices; I think it would be better to have two parts to the question. First: "Choose the answer that makes the most sense in this sentence" followed by multiple choices, then when that answer is chosen the second part would be: "What grammatical device did you use?" followed by another multiple choice listing different devices like noun, pronoun, preposition, etc.
What I think this would achieve is helping native English speakers, like myself, learn what grammatical devices they are using. For a lot of us we can choose the correct answer because we know what sounds right without knowing that it is a preposition or adverb we are using.