(you can find a word game on this website!)
So I don't want to hear any complaints that I don't know that rule!
Read what Grammar Girl has to say about it -- it's basically what I finally came up with on my own. "Awhile" is an adverb. "I stayed awhile." "He stared at the girl awhile and then approached her."
"A while" is simply an article plus a noun, and that construction is required when an object is involved, for example, in prepositional phrases: "I stayed for a while." "He left after a while." Grammar Girl gives this example, which may confuse some people. "It's been a while since he visited." The reason you use the noun form here is that "to be" in a copular, or linking, verb and takes a predicate nominative or a predicate adjective rather than an adverb. (You wouldn't say, "He's been quietly for a while,' would you? You would say, "He's been quiet for a while." "Quiet" is an adjective modifying "he.") Esoteric, you say? You should have heard my mother expounding on linking verbs! Some other linking verbs are "to become," "to feel ," to smell," etc. If you're interested in pursuing this further, go here.