Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of for-profit education company Apollo Group (Nasdaq: APOL) got an "F" from investors today, falling as much as 16% in intraday trading after the company updated its 2012 guidance.

So what: If colloquial English were the standard for corporate communications, today's press release from Apollo might well have read, "Whoops! We're not going to do as well as we thought this year."

The parent of University of Phoenix told investors that -- after adjusting for an extra day in the second fiscal quarter of 2012 -- new student enrollment will show a YOY decrease "in the low to mid-single digits." The company had previously thought that it'd see enrollment growth for the period. And even though the company is keeping its revenue guidance for fiscal 2012 the same, it lowered its operating profit guidance to a range of $625 million to $725 million. At the midpoint, that's roughly a 4% decrease from previous guidance.

Now what: The entire for-profit education sector has been under pressure ever since the government -- which finances a good deal of the students populating those schools -- has cracked down on many questionable practices. Based on the market's reaction today, it seems that investors were expecting a much more robust recovery for Apollo in particular and they're still very sensitive to bad news.

While the 16% stock drop suggests disaster, the 4% downward earnings revision isn't particularly severe. That said, it's more concerning that new enrollment -- which portents future performance -- is expected to drop this quarter.

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