It’s in the first panel of this Mr. Fitz, which has a student speaking, whom I wouldn’t be surprised to see making this mistake. It’s easy to make. Do you see it? (It’s not the extra “a” in the second sentence; that’s just a typo.)
Hint: The mistake has to do with agreement.
Okay, I won’t go into all the details about the full construction of this sentence, but “us” and “an adult” are equivalent. Hence, they should agree in number, meaning both singular or both plural, not one of each.
He should have said, “…teaching us to be adults” or “teaching me to be an adult.”
See how the agreement makes the sentence a little smoother?
Go thou and do likewise.
PS—Since I started with a test, I’ll end with one. It also has to do with agreement. Here’s a sentence from an email my wife sent me:
It’s nice to know that someone else besides you & Dave knows how busy I actually am.
Okay, should “knows” stay singular or be changed to plural?