First, i usually make my questions from what I have been teaching them in class every week.  I make my lessons based on what I can use for effective exam questions as well.  I teach them enough to where I can make an interview based exam for the students.  It is usually two or three questions and they only talk for two or three minutes each.  Now, I have to make this usually very simple questions, since the number of students is such a large number.  It is hard to do all 400 to 900 students in one or two weeks of testing. 

I will say that you'd better be ready for some hard times ahead when it comes to your exams.  Those were the hardest two weeks I have ever done at public school.  Not to mention, I had to do it for two semesters.  You'd better make sure to have enough red bull on hand because it is going to drain you big time.  Good Luck