Sorry, but they do not know the parts of speech. All the remedial text books for college students try to teach the parts of speech as well as two other things that are totally surprising.
Speaking of how difficult it is to teach young folks, you keep repeating this nonsense even though I've explained it to you at least twice. You are trying to teach them about something that they already know. If they didn't know the parts of speech then they would NOT be able to speak in grammatical sentences.
You're confusing the naming of the parts of speech with knowing the parts of speech. Now, if you mean to suggest that you are teaching students about
language, that's one thing.
If we changed the names of all the parts of speech tomorrow, you wouldn't know them either. Would that mean that your speech would immediately become a jumble of disjointed words, that you wouldn't know what parts of speech to choose when you spoke, that you wouldn't be able to follow the rules of English grammar?
The first is that the object of a preposition is never the subject of a sentence.
Why do you suppose a teacher of the English language is so guarded in her discussions of language? Describe exactly what you're getting at and provide examples?
When I first saw those lessons, I thought no one has trouble with that. I was very wrong. You have no idea what a struggle it is to teach prepositions to college-aged students who weren't taught them before.
You think that these kids reach the age of 18 or so without full knowledge of prepositions. What a ludicrous notion! Do you think in their speech of the previous 15 or so years that there has just been a void when a preposition was required?