Excerpts from nbcchicago.com:

Eighteen ambulances responded to a pep rally at Morton West High School in Berwyn Friday afternoon after nurses became inundated with students reporting heat-related illnesses.

Berwyn Fire Chief Dennis O’Halloran said the calls of heat exhaustion started coming in around 3 p.m. The students were in the school’s stadium. Six patients were transported to hospitals and one signed a release form to go home with their parents.

Anyone else in the stadium that did not go to the hospital was sent home. A walking parade between Morton West and Morton East high schools began at 1 p.m. but it was unclear if those students were sick.

Eight other agencies responded to the school, O’Halloran said.