CHICAGO (AP) — A forecast featuring warnings of excessive heat has forced Chicago Public Schools to cancel summer school classes for some students.

Schools CEO Jean-Claude Brizard called off classes Thursday at 10 schools that don't have air conditioning.

In a statement, Brizard says the district determined the cancellations are in the best interest of students and staff.

Chicago is the nation's third-largest school system with about 405,000 students and more than 675 schools.

The schools closed Thursday are Altgeld, Attucks, Bennett, Courtenay, Faraday, Gregory, Holden, Penn, Stevenson and Harold Washington.