“Don’t smile until Christmas” is a sound bite of wisdom passed down through generations of teachers.
It’s not really about smiling.
It’s about breaking character and letting your guard down too early. (More detail on this in the See Me After Class chapter called Your Teacher Personality: Faking it. Making it.)
Some teachers are strict the first few days, but then relax because the kids seem to be behaving.
By the time they realize it’s too soon, it’s too late.
This advice should really be “Don’t smile, let kids know you have a first name, let kids know you have ever cried or uttered a curse word, or allow kids to imagine you doing anything besides teaching and grading papers—until Christmas.”
Just remember: the first few times you think your class is under control and it’s okay to relax, you’re probably wrong.