Talk to Elisa and Antoine. Walk to the library to find out it is locked, then walk to the girls' dormitory hallway and talk to the Foreman. Then, find out you are not locked in. Go back to the Chat Room and talk to Antoine, asking for his sandwich.
Go to the Lecture Room, talk to the Principal, and get the key. Retrieve the book from the computer table. Bring the book to Antoine. Accept the cheese sandwich. Bring the cheese sandwich to the Foreman. Walk into Elisa's room and get the stationary, which is on the far back table. Walk back to the Chat Room. Give Elisa the stationary.