Then another 15 or so cases were reported in the school's upper division.
The outbreak motivated school officials to shut down the Lower School for a few days and shift the Upper School to virtual learning.
Head of School Patrick Fitzpatrick says it was simply the right thing to do.
"It's not so much a matter of a certain number of students who were sick, but this has been our biggest outbreak. And so, we felt like we needed to respond in this way," said Fitzpatrick.
Fitzpatrick says he is just glad the situation didn't take a real turn for the worse.
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"As far as I know," he says, "no one has been hospitalized and the COVID sicknesses have been very minor."
Plumstead Christian School parent Tracy Spiaggia says she's very happy with the way the school handled this COVID-19 outbreak, primarily because the school included parents in the decision-making process.
"This can be handled well if people collaborate and, like I said, just kind of don't pit one person against another. Just try to be as open and rational as possible," she says.
In the meantime, Fitzpatrick says the school will continue to adhere to the statewide COVID protocols as long as they remain in place.
"We are complying with the mask mandate. That mask mandate does allow for mask exceptions, and quite a few of our families have mask exceptions for their students," added Fitzpatrick.
With the exception of the preschool, the lower division returned to in-person learning Monday.
The upper division, grades 6 through 12, is expected to return to in-person learning this coming Thursday.