The S&P 500 managed to pull out its fourth consecutive week of gains last week, rising 0.58% to 1,166.59. The gains came despite a big week of volatile news, including the passage of the long-debated health-care bill, concerns the U.S. government would no longer be able to finance its deficit cheaply, and jitters surrounding sovereign debt in Europe.

Pops and drops
Here are the five biggest S&P 500 upticks and five biggest S&P 500 drops of last week (measured Friday close to Friday close):

Winners on the week:

Company

Percentage Gain on the Week

Lennar Corp (NYSE: LEN)

13.6%

Cliffs Natural Resources (NYSE: CLF)

11.3%

Genworth Financial (NYSE: GNW)

11.1%

Citigroup (NYSE: C)

10.5%

Titanium Metals

10.2%

Source: Capital IQ (a division of Standard & Poor's).

Losers on the week:

Company

Percentage Loss on the Week

Genzyme Corp (Nasdaq: GENZ)

(10.8%)

NRG Energy (NYSE: NRG)

(8.2%)

Chesapeake Energy (NYSE: CHK)

(7.6%)

CONSOL Energy

(6.7%)

National Oilwell Varco

(6%)

Source: Capital IQ (a division of Standard & Poor's).

A closer look
Shares of Lennar got a boost last week after the homebuilder posted a narrower-than-expected first-quarter loss on a 6% increase in the average price per home sold and lower expenses. Revenue slipped 3% in the quarter, but orders rose 18%. The company said it is on track for a profit in 2010. Lennar is reaping the benefits of the actions it took early on in the recession to shore up its financial position. The company also had the foresight and wherewithal to purchase land at cheap prices to position itself for the recovery. These actions have already led to fatter profit margins.

Also helping Lennar -- and other homebuilders -- rise last week was news that Bank of America will begin modifying the principal balance of some loans.

Meanwhile, Citigroup shares leapt after Bloomberg News reported that the government is in the process of arranging a plan to sell its 27% stake in the embattled bank. The plan, which could be revealed as early as next month, would lock Citi into a preset schedule for selling its shares. The set schedule is being put in place to quell any concerns that the government is selling on inside information that could be misconstrued as negative for the company.

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Fool contributor Jennifer Schonberger does not own shares of any of the companies mentioned in this article. You can follow her on Twitter. Chesapeake Energy is a Motley Fool Inside Value selection. National Oilwell Varco and Titanium Metals are Motley Fool Stock Advisor picks. The Fool owns shares of Chesapeake Energy. The Motley Fool has a disclosure policy.