A blast of late summer heat caused disruptions Wednesday for schools from Michigan to Virginia, with some districts dismissing students early and others holding classes online just days into the new academic year.

While temperatures weren’t as high as last month’s triple-digit deadly heat wave, schools in states including Michigan, Maryland, Pennsylvania and New Jersey cited inadequate air conditioning in cutting days short. One Massachusetts district canceled two days of classes because of hot classrooms. Temperatures in the mid-90s also led to online learning in Pittsburgh and Baltimore.

Only 20% of public schools in Detroit, where the temperature reached 89 degrees Tuesday but dropped Wednesday, have air conditioning. The district dismissed its roughly 54,000 students three hours early Wednesday for the second consecutive day.