There's never a shortage of losers in the stock market. Let's take a closer look at five of this past week's biggest sinkers.

Company

Nov. 23

Weekly Loss

My Watchlist

K12 (NYSE:LRN)

$16.27

20%

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Best Buy (NYSE:BBY)

$11.70

15%

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Scholastic (NASDAQ:SCHL)

$26.39

15%

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Cliffs Natural Resources (NYSE:CLF)

$31.23

12%

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Diamond Foods (NASDAQ:DMND.DL)

$13.28

12%

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Source: Barron's.

K12 got schooled after a Wells Fargo analyst's downgrade. The firm cooled on the Web-based education provider after problems with its Colorado Virtual Academy charter. It's been a rough time for investors in for-profit educators. Most of the attention has been given to the post-secondary players with virtual college programs, but K12 shows that you can still flunk out at the grade-school level.

Best Buy was unplugged after another disappointing quarterly report. The consumer-electronics retailer saw its shares fall to its lowest levels since the turn of the millennium. Sluggish same-store sales and a tiny adjusted profit don't make for the kind of momentum that Best Buy needs heading into the critical holiday shopping season.

Scholastic earned a dunce cap after the publisher of kid-friendly books hacked away at its outlook. For its fiscal year ending in May, Scholastic now sees a profit of no more than $1.60 a share. Its previous guidance was calling for earnings per share to clock in between $2.20 and $2.40.

Cliffs Natural Resources stumbled after revealing that it plans to shut down some stateside production and delay an expansion at a Canadian iron ore mine.

Diamond Foods was also cracked open after an analyst downgrade. Jefferies & Co. talked down the company's prospects given the lack of earnings visibility. The analyst's new price target of $10 is well below where the stock sits now.