PARK RIDGE, Ill. (CBS) — At least a dozen students at Maine South High School in Park Ridge have tested positive for COVID-19, the school district confirmed.

Parents were issued a letter saying on Friday, the building administration at Maine South was notified of potential coronavirus exposures at multiple parties across a four-day period that began the previous Friday, Aug. 14.

After spending the whole weekend calling families, the school learned that students had been exposed to the virus at the parties. The school attempted to conduct contact tracing – either contacting or attempting to contact 71 students – but not all families cooperated.

Based on the number of students believed to have been in attendance at the parties, the school moved several events online – including senior day, which was held on Monday; junior orientation on Tuesday and Wednesday; and sophomore orientation on Thursday and Friday.

Classes were virtual for students of all grade levels at the school beginning Tuesday. Students who receive special education services still came to campus as planned.

“When your student is being tested for COVID, we need to know about it immediately,” the school said in a letter to parents. “Please call the school’s health office when you take the test and then again with the test result. Information can be found in our COVID parent guide.”

The school also expressed disappointment from families that either refused to share information or gave false impressions of what happened when the school attempted to contact trace.

“There is no disciplinary action when we have to contact trace and when we call, we are doing so to keep our students and staff safe and make sure COVID is not passed along to anyone, especially those with underlying health conditions,” the school said.