Teachers assistant. Co-teacher.
The first - the thing I am officially called (and paid to be, for that matter).
The second - the thing I am called in front of the Prob Stats class that I TA for.
There were quite a few reasons for the slightly elevated title (it was a decision made by my boss, not me). The most pressing was that I will be teaching a couple of lectures a month while she's out of town, and they're more likely to respect me if I'm not called a TA.
The first of those lectures is next week.
These students, who seemed so young the first week, now seem sort of ... scary. They're smart and stuff.
They ask hard questions.
If I were a TA, I could say 'sorry, I'm just a TA'.
Obviously, calling me a teacher was a terrible idea.