I used to believe that the room number for a class was to indicate what grade was in the room. E.g. Rm. 5 - Gr. 5. I stopped believing this when I got to middle school and was in room 212.
A childhood belief about classes

others believed things like this
- I used to believe Jesus cleaned my room.— Angelina
- I used to believe that when we left a room the TV set started to speak about other things — Nur
- I used to think that the upper struture on the caboose was the rest room.Anon
- I used to believe the living room furniture would party after we all went to sleep.— Ellen
- I used to turn the TV off when I left the room so I didn't miss anything.— S.Lee
- My older brother used to tell me that if I "untied" it, I'd fly around the room like a balloon. — Gullible youth