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 private post-secondary school Education Management (Nasdaq: EDMC) are heading into graduation season on wobbly legs, posting a brief 5% gain followed by an equally quick 10.1% drop. In the end, the stock settled around 2% above last night's closing price, all on feeble trading volume.

So what: There isn't much going on in paid-education land today. Rival ITT Educational Services (NYSE: ESI) saw a similar low-volume decline, though without the severe spike-and-drop swings of Education Management.

Now what: ITT's much higher average trading volume probably saved that stock from Education Management's flailing today. Low-volume stocks are easily manipulated, whether intentionally or not, and an even lower-volume trading day just magnifies the liquidity problem. This is why we Fools always prefer set-price limit orders over more random market orders on that class of investments.

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