Chicago ? 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.