Senior portraits are often well-planned, professional photoshoots. They signal the end of the school year and the transition into adulthood. At Farmington High School, they have a different tradition.

Sofia Nielsen, a graduating senior at Notre Dame Academy in Staten Island, New York, spent two months sketching portraits of all 110 of her classmates.

A new social media challenge seems harmless: It asks people to share their senior year portraits to show support for the class of 2020, who may finish high school in quarantine due to the ...