Twenty desks - enough to fill a classroom - sat empty in a downtown plaza Tuesday, each bearing a pair of sneakers and representing a Chicago Public Schools student killed by gunfire this school year.

Several hundred more sat empty in city schools, as busloads of teens skipped classes to attend a gun-control rally - their absences sanctioned by the district, whose CEO says he's angry that too many students talk about "if" they grow up, instead of "when."

"This doesn't happen in other countries," Arne Duncan said. "We just value our right to bear arms more than we value our children, and our priorities are fundamentally backwards."

Since September, 20 students in the nation's third-largest school district have died in shootings. Last school year, 24 students were shot to death, compared with 10 to 15 in the years before.

The most recent fatality involved an 18-year-old killed in a high school parking lot last weekend. That school, Simeon Career Academy, sent 10 busloads of students to the rally in front of the James R. Thompson Center, which houses state offices.

Students from three other high schools participated, many wearing letter jackets or heavy coats on a gray, unseasonably cold day. Several families whose children have died recently in gun violence also attended the rally, as did Gov. Rod Blagojevich and Mayor Richard M. Daley.

While some in the crowd of several hundred teenagers horsed around, laughed and chatted with friends, others somberly carried placards with victims' names, or signs reading "Save Our Children - Follow the Guns."

Other students used their cell phones to take pictures of the empty desks that sat in front of a podium.

Chaqueta Clifton, 16, wore a button on her pink jacket reading "Stop Killing People." She said her father was killed in a robbery when she was 7, and her uncle and cousin died in gun violence as well.

She said the recent deaths of CPS students have made her "kind of paranoid." She tries to be hyperaware of her surroundings, and stays clear of any fights that break out nearby, saying some of the shootings have been the result of petty arguments that started out as "nothing."

"It makes me angry, and sad, and I just want to do something about it," she said.

Among the gun-control measures rally participants demanded were a limit of one gun purchase a month, a renewal of the federal assault weapon ban, and background checks for all gun sales.

Chicago bans handgun ownership and sales, and Daley regularly pushes gun-control measures at the state Capitol in Springfield, where lawmakers are divided more by geography than political allegiances. Legislators in and around Chicago tend to favor gun restrictions, while others usually argue for hunter and gun owners' rights.

Blagojevich urged the rally's participants to make their voices heard in Springfield and Washington. "How many more children have to die before the men and women who make the rules wake up and start responding to the needs of communities and kids that go to our schools?" he said.

National Rifle Association lobbyist Todd Vandermyde said he questioned whether students should be taken out of classes "to serve as cheerleaders for a political stunt."

Chicago "has some of the strictest gun control in the nation ... They said this was going to solve the crime problem, and their panacea hasn't done anything but disarmed law-abiding citizens," Vandermyde said.

None of this school year's killings had occurred on school property until last weekend's. Even so, the Chicago Police Department already was planning to increase school patrols and soon will have live access to thousands of security cameras mounted outside and inside schools.

Several students at the rally also called for more highly trained security guards at schools, while others expressed worries that no amount of gun control would keep gang members from acquiring guns.

"They'll always find a way," said Tiara Irby, 17.

(This version corrects that all but one of this year's killings happened off school grounds.)