Stocks pulled back from Wednesday's regular-session surge after the closing bell, but

Hoku Scientific

( HOKU) booked spectacular gains.

Shares skyrocketed 74% to $8 after the Hawaii-based clean-energy developer

struck a lucrative 10-year polysilicon-supply deal

with Chinese solar-power company

Suntech Power

(STP)

. Suntech will pay Hoku up to about $678 million depending on milestones and other conditions, including an initial $2 million deposit on signing and $45 million in product prepayments. Suntech recently tacked on 9 cents at $32.37.

Another late winner was Iowa-based

Casey's General Stores

(CASY) - Get Report

. The convenience-store chain added 5.7% after continuing-operations income surged 63.6% year over year to 36 cents, or $18 million, in the fiscal fourth quarter. Stripping out a one-time 6-cent gain, this topped the average Street estimate by 4 cents a share, per Thomson Financial. Revenue, at $1 billion, edged out two analysts' estimates. Shares were up $1.53 to $28.20.

Among the postbell laggards, however, was

Select Comfort

(SCSS)

. The Minneapolis bed maker dropped 6.4% to $15.89 after slashing its full-year earnings outlook to range between 87 cents and 93 cents a share, "given current trends" exemplified by an expected year-over-year sales decline in the second quarter. Prior guidance pegged per-share income at $1.02 to $1.09. Wall Street is looking for $1 per share.

Capstone Turbine

(CPST) - Get Report

meanwhile slid 13.4% after posting a loss of 6 cents a share in the fiscal fourth quarter, which missed the sole analyst's estimate by a penny. Despite halving its losses year over year, the Chatsworth, Calif., microturbine-systems maker lately traded at 97 cents.

California's

Computer Sciences

(CSC)

sank after saying an earnings restatement cut its per-share profit by 12 cents in fiscal 2007 and by 48 cents in fiscal 2006, due to previously announced accounting errors. Despite

beating earnings estimates

in the quarter ended March 30, the information-technology firm was off 2.8% to $54.48.

And

Blackboard

( BBBB), a Washington, D.C.-based education-software company, said it will sell up to $150 million in convertible senior bonds along with an underwriters' option for up to another $15 million to cover overallotments. Shares slipped 3.4% to $41.40 in recent trading.