By CBS3 Staff

GLEN MILLS, Pa. (CBS) — A big schedule change tonight for some middle school parents. Garnet Valley Middle School in Delaware County switches back to all-virtual learning tomorrow.

In a letter obtained by Eyewitness News, the district says the school has had 18 cases of COVID in less than two weeks.

Students will stay virtual the rest of the week and return for in-person learning next Monday.

Meanwhile, an investigation is underway after a COVID-19 outbreak at Penn Valley Elementary School in Montgomery County. Lower Merion School District officials say a faulty HVAC system may be to blame for the outbreak.