she goes to another school

What boys say when they are caught in a lie about having a girlfriend

Boy 1: I have a girlfriend now.
Boy 2: Then who is it?
Boy 1: She goes to another school.
Boy 2: So she doesn’t exist.

She goes to another school

Used when someone is clearly making up an excuse for something. Derived from the kids who would always claim they had a girlfriend but that "you wouldn't know her, she goes to another school".

Jack: I'm usually good at throwing a frisbee, it must be the wind.
Elliot: Yeah dude totally, "she goes to another school".