CHICAGO - When city students arrived for the first day of school under the blazing temperatures of a Midwest heat wave, staff greeted them with some unusual school supplies: water bottles, fans and wet towels to drape around their necks. What they couldn't always offer was air conditioning. "It's kind of hard to focus because everyone was sweating," said Deniyah Jones, a 12-year-old 7th-grader at Nash Elementary School on Chicago's West Side, which has just a few window units for the entire fortress-like brick and stone building. This year's late August heat exposed a tug-of-war in school districts that are under pressure to start school earlier than ever but are unable to pay to equip aging buildings with air conditioning. Parents who worry hot classrooms are a disadvantage for their kids are issuing an ultimatum: Make classes cooler or start the year later. "Thinking about air conditioning - we can't even afford new textbooks," said Bement Community Unit School District Superintendent Sheila Greenwood, who oversees a tiny district of 380 students about 20 miles southwest of Champaign, Ill. Many people can recall school days spent inside ancient, brick-construction buildings that on sweltering days seemed as hot as pizza ovens. But hot classrooms are becoming a bigger problem for schools than in years past, and increasingly, getting a "heat day" is as common for students as a "snow day."