grammar - "A person skillful at what he does" vs. "A skillful person at what he does"

I was helping a friend with an ESL test, and the question was looking for the answer "Practice can make a person skillful at what he does". One of the students answered with "Practice can make a skillful person at what he does", and my friend asked if this was definitively wrong, and why. I didn't have a definitive answer, other than "I think it's wrong because it sounds awkward." Is there a grammar rule that can clarify this?

Answer

In the first example, the portion of the sentence under question is "to make (something) skillful". It can be broken down roughly like this:

(Practice can) (make (a person) skillful) (at what he does)

The placement before a noun of "skillful" in the second sentence, however, has removed it from the verb, and reduced it to a simple adjective.

(Practice can) (make (a skillful person) ...) (at what he does)

Since the idea of "making a skillful person at what he does" makes no sense, a native speaker is left with a feeling that the sentence is incomplete. Practice makes a skillful person what at what he does? I add the ellipsis to show where the gap is.