Some dark house

Every now and then, the cram school which I work for sends some new teachers to my class. They at all times step into the classroom in the middle of my instruction, so it's easy to know who they are and what their purpose are for. They probably just want to get some ideas of how they can teach in the near future by observing others.

In the first place, I thought they were just like some new comers in my class. Then I found their language fluency was too good to be a student. Here comes an real example; a lady, who I assume is a teacher to-be, came to my class the other day, finding her seat in a calm and unhurried manner. She spent only about 10 minutes accomplishing her writing as the class for that night was a writing practice for GEPT. I looked at her essay, pretending she was a "real" student. Leaving some comments on her work, I told her she did a great job and was supposed to be no problem getting a great score on GEPT writing test. She thanked me and then left the classroom in a snap as she had already finished her assignment in class. Kind of fun but no harm to me, though. There are always dark house in my class while many of them shouldn't be there.

every now and then = from time to time 不時的
at all times = all the time 總是
In the first place 一開始
new comer 新人, 新進者
a teacher to-be 即將為人師的人
calm and unhurried 從容不迫的
be supposed to 應該
in a snap 迅速的
dark house 深藏不露之人