This could take a while…

English language learners struggle when commonly confused words pop up in reading and writing. Much like any time and anytime, a while and awhile have similar meanings and sound the same, but have different parts of speech. So when exactly do we use these terms?

A While

Meaning:	a period of time
Pronunciation:	/æˈwɑyl/
Part of Speech:	article + noun
Sentence Positions:	the object of a verb (V + O) after a preposition (Prep + N)
Examples:	It has been a while since I saw that movie. Bread will go stale after a while. We will leave in a while.

Awhile

Meaning:	for a short time; for a while
Pronunciation:	/æˈwɑyl/
Part of Speech:	adverb
Sentence Positions:	after a verb (V + Adv) at the end of a sentence (SVO + Adv)
Examples:	I need to rest awhile. We waited awhile, but she never showed up. I'm just going to stand here awhile.

Tips & Tricks

If you can replace it with "for a while," use awhile. For example, The Chicago Manual of Style's FAQ had a great answer to a debate about take a while vs. take awhile (correct answer: take a while).

It is true that either an adverb or an object can follow a verb. But the adverb awhile means for a while, which clearly should not follow take (compare stay awhile, which survives expansion to stay for a while).

It took awhile. = It took for a while.
We stayed awhile. = We stayed for a while.

I also found a great tip on Grammar Girl's Quick and Dirty Tips blog. If you can replace it with a noun about time, use a while. If you can replace it with an adverb of manner, use awhile.

It's been an hour. = It's been a while.
Go play quietly. = Go play awhile.

Oxford Dictionaries has a good usage summary to share with your learners if they're still confused:

The single word awhile is an adverb meaning "for a short time," and should not be confused with the noun use of a while, "a period of time": stand here awhile, but we stood there for a while

We stood there awhile.
We stood there for a while.

Awhile or A While After a Preposition?

Can awhile be used as the object of a preposition? This is something I would only discuss with my higher-level learners. Merriam-Webster's Dictionary says that awhile is often seen and heard in this position, but warns that grammar sticklers consider it to be incorrect.

We sat around and talked for a while. (correct)
We sat around and talked for awhile. (okay, but considered wrong by some)

Your higher-level learners should also be aware that if the preposition is part of a phrasal verb or verb + preposition expression, then we need to use the adverb awhile. (This also follows the handy tip about using awhile when we can replace it with for a while mentioned above.)