Several hundred Chicago public school students have rallied to remember classmates killed by gun violence this school year.

Politicians, school officials and church leaders joined the students Monday to call for stiffer gun control measures.

Chicago school chief Arne Duncan says he runs into too many students who talk about "if" they grow up — instead of "when" they'll grow up.

Duncan says he's proud of all the students who chose to attend the rally outside the Thompson Center.

Since September, 20 Chicago Public Schools students have been killed by gunfire. The latest was an 18-year-old killed in a high school parking lot over the weekend.