Greely High School in Cumberland will switch to remote learning Thursday because of multiple COVID-19 cases revealed by pooled testing.

In most weeks, pools typically come back with no more than one positive case, but this week’s result showed a “significant increase,” said School Administrative District 51 Superintendent Jeffrey Porter in a notification sent Wednesday to community members.

“Contact tracing is underway with each of the current positive pools, but one case at the high school is complicated and will require extensive tracing that cannot be completed before school starts tomorrow,” Porter wrote. “Therefore, as a precaution, Nov. 18, will be a (remote learning day) at Greely High School.”

Porter said all other schools in the district covering Cumberland and North Yarmouth will have in-person learning Thursday, and moving a school to remote learning “is a last resort and is only done when there is not another viable option.”

He said he remains hopeful that Greely High School can return to in-person learning Friday.

The superintendent said that pooled testing of students has helped the district identify COVID cases and prevented spread to other students and staff members. Greely High serves about 650 students in grades 9-12.