Principal Steve Bild said in the letter that several safety measures had been implemented during the day.
"We are relocating students from our hottest classrooms, which are generally located on the second and third floors, to one of the air conditioned common areas. The library, cafeteria, auditoriums and band rooms are all air conditioned spaces that will be in full use today," Bild said.
Students were also encouraged to drink extra water and to bring bottled water to class. School nurses were instructed to look for symptoms of heat-related illness.
All after-school activities and athletic practices are scheduled to run as usual, and will be equipped with cooling stations with ice and shade, Bild said. If the practice schedule changes, parents will be notified as soon as possible.
The excessive heat is expected to continue Wednesday, according to the National Weather Service.
"While we hope that the hot spell breaks soon, the forecast for tomorrow also looks very warm. We will continue to monitor the heat levels in our building and keep you posted on what we are doing to help students," Bild said.
The National Weather Service is forecasted a high of 97 degrees and a heat index of 100 Tuesday. That's hotter than the record high of 95 degrees, set in Chicago on Sept. 10, 1983. According to AccuWeather.com, the last time a record high was set in September for Chicagoland was 1998.
The high for Wednesday is 89 degrees, with a 30 percent chance of showers and thunderstorms int he afternoon. Thursday will be mostly sunny with a high near 79.
Relief could come late Friday as a cold front approaches, bringing the high down to 65 degrees and the low to 49, according to the NWS.