This contains spoilers for Another, which is somewhat new (the anime is from 2012).
Another is an anime series about a cursed classroom. The students (and teachers) have designed a countermeasure to avoid the curse from triggering each year, which consists on completely ignoring a student (treating them as non-existent). By doing this, the number of students in the classroom is technically decreased by one, which makes up for the extra dead student that got mixed in the class.
Misaki is the chosen student to be ignored by the classroom this year. After a mess up, Sakakibara is also ignored.
However, if I'm not mistaken, during exam periods, both students (Misaki and Sakakibara) have exam papers. Why? Doesn't giving them exam papers pretty much acknowledge that they exist? Doesn't that break the entire countermeasure? (from the point of view of the classroom)
For clarification: the countermeasure involves people directly related to the class. This means, students that belong to this classroom and teachers that teach this class. External students and teachers from other classrooms are not involved with the curse, so they may interact with the non-existent students just fine.
The librarian, and students from the art club etc, have no problem interacting with the non-existent students.
The external students/teachers are not very well aware of the curse though. The cursed classroom tries not to talk about it with others.