670 to 480!

Looks like you got your answers already but here is a different take:

You should be fine without a retake (you can always explain in an optional essay if you need to) - what are your target schools? (of course if you can retake and get 700+ that's better but what are the chances)

What were your practice scores before the retake?

How much time passed between the 2 attempts?

I just applied to Wharton, 100% won't get in but whatever. Other schools I'm looking at are UT, USC, NYU, WashU, Emory and UCLA. Probably won't apply to all, but at least a few of them. NYU would be a dream school but UT would be ideal.

I took mostly Kaplan tests. My diagnostic was a 530, this was considering I have never seen any type of GMAT question before. I eventually started scoring around 630 on the Kaplan tests. I took a MannhattanGmat test last week and scored a 600. The 670 I got the first time could have been luck, but dropping to 480 is just ridiculous.

I took my first test in November 2011 and I took the second one yesterday. So about 2 months have past.

Is it possible to not report the 480 to the schools that I gave my scores on my first attempt at the test?

anyone?

I am not an expert on this, unfortunately. But Gyanone seems to suggest that the first 5 schools would see only your first scores - so you should be fine there.

Probably you could ask Stacy Blackman on the 'Ask Stacy' thread to confirm?

For the second batch of 5 schools, you can possibly explain your substantially lower score on the second attempt in your optional essays with something like 'took the test while I had very high fever' or some other personal emergency...? They might just buy it, because a ~200 point drop is pretty unusual and they might believe that something was really amiss the second time around.