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: Apollo Group (Nasdaq: APOL) dropped 10% in intraday trading today after missing earnings expectations and issuing disappointing guidance.

So what: Second fiscal quarter EPS of $0.45 was down 25% from the year-ago quarter and badly missed the consensus estimate of $0.69. Management now expects operating income excluding "the impact of special items" of $1.15 billion to $1.20 billion for fiscal 2011, which ends in August 2011, and $675 million to $800 million in fiscal 2012.

Now what: Revenue is expected to decline from $4.93 billion in fiscal 2010 to between $4.65 billion and $4.75 billion in fiscal 2011 and between $4.00 billion and $4.25 billion in fiscal 2012. Management noted it is changing its approach in response to Congressional and Department of Education concerns about student loan defaults, dropout rates and student debt and that the "outlook does not reflect the unknown impact of future regulation, including the proposed regulations relating to 'gainful employment.'" The stock may look cheap at a forward P/E ratio of 9.9x, but industry changes suggest it is a value trap.

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Fool contributor Cindy Johnson does not own shares of any company named above. We Fools may not 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.