The museum is now analysing the damage to the painting "Portrait of Una" by the Russian artist Kazimir Malevich, before deciding whether to contact the police.
"It is very regrettable. I don't want to speculate on what will happen before we make our assessment," Gabriel Gunnarsson at the museum press office told the newspaper.
The class, from Igelstaviken High School visited the museum on October 7th. The museum subsequently discovered that a line had been drawn on the painting.
The museum is unable to specify what the Malevich is worth, as it is part of the permanent collection and has thus not been valued for sale.
The school's principal has been in contact with the pupil's parents in connection with the incident, and is awaiting the result of Moderna's assessment of the damage, Länstidningen Södertälje reported.