Contains the letter of a girl named Sue (school nickname "Susquehana Sue") sent to her aunt from her seat at school: #7 Callahan Row,
R Flat (explained as Mrs. Ropers flat / apartment; Mrs. Roper was her teacher); her desk was the 7th in the row in which a girl named Callhan sat at desk #1.
This was described in the letter as the way the students ID'ed the desks, not the teacher or the school.