Around 140 pupils at the Linnanjoki school in Porvoo did not show up for classes on Monday following the previous day's news that 17 students and four teachers at the institution were sent home to continue distance learning after a child at the school tested positive for a coronavirus infection.
The school, located about 50km east of Helsinki, serves around 540 pupils.
The institution's principal, Päivi Outinen, said that some of the students had already applied for permission to continue distance learning before being called back to classes last Thursday, when the government re-opened schools.
She said students may be permitted to be absent from classroom-based teaching for reasons including health-related issues or family holidays.
Outinen said she was unable to say how many students were absent due to Sunday's news about the confirmed coronavirus case at the school, however.
"Currently about 400 students are onsite at the moment, and a small number are absent, but most are here," Outinen said.
Some parents had reached out to the principal about the coronavirus situation, she said, but noted the questions were "practical," with parents simply wanting clarification and information about the situation.
Outinen said that the school has been following safety guidelines given to institutions across the country as they reopened classrooms. She added that pupils are kept in separate groups, and that contact with other student groups and faculty members is restricted.
She said classrooms are set up so that students have adequate space between one another, as well.
The principal also said that she has spoken to the guardian of the pupil who tested positive for coronavirus and that the student is doing well.
The 17 other students who may have been exposed to the virus will continue the school year from home until the end of the school year, 31 May.