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 Apollo Education Group Inc (NASDAQ:APOL) were getting an "F" from investors today, falling as much as 14% and closing down 9% on a rumor that hedge fund manager Bill Ackman has taken a large short position in the stock.

So what: The parent of the University of Phoenix started falling shortly after 11 a.m. as word spread that Ackman's Pershing Square fund was soon to announce a short position in the for-profit educator. Trading volume in Apollo shares was nearly six times its normal level, though it's unclear when the shares would've been shorted. The education sector was falling across the board today as peer ITT Education Group withdrew its guidance as it awaits a decision from the SEC that could affect some of its previous results.

Now what: There was no confirmation of the Ackman short, so for now the news remains just a rumor. While Ackman is one of the more closely followed hedge fund managers, he has a made a number of big-time blunders recently, including backing J.C. Penney and former CEO Ron Johnson and shorting Herbalife, whose shares are up close to 50% since he announced his position. Apollo, like much of the education industry, is struggling with declining enrollment, which has sent revenue and profits plummeting. Whether or not Ackman is short, expect the company's fundamentals to continue driving the stock, not the opinion of one investor.

Apollo was once a multibagger. Will this stock be your next one?
Give us five minutes and we'll show how you could own the best stock for 2014. Every year, The Motley Fool's chief investment officer hand-picks one stock with amazing potential. But it's not just any run-of-the-mill company. It's a stock perfectly positioned to cash in on the upcoming year's most lucrative trends. Last year his pick skyrocketed 134%. And previous top picks have gained upwards of 908%, 1,252% and 1,303%! You don't want to miss what could be his biggest winner yet! Just click here to download your free copy of "The Motley Fool's Top Stock for 2014" today.

Jeremy Bowman and The Motley Fool have no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.