It's one thing to design a fantastic, student-centered course. It's a whole other thing to make that course work in a real-time setting. To make it work, at least for my large course, requires a team of teaching assistants. For just under 400 students I was assigned 4 TAs. Initially, I was given two TAs and I had to campaign vigorously for the "additional" two. I found it deeply irritating that I was having to organize letter-writing campaigns to the deans in my college so that there would be enough classroom help to actually implement the student-centered class that I had worked so hard to create (and that the college had spent at least some money to support). Sure, two TAs might have been sufficient when I was standing in front of the class lecturing and encouraging the students to be passive vessels; but the whole point of the redesign was for them to be active and engaged. Beyond classroom logistics "stuff", I needed TAs to help me by walking around and dropping in on the "turn to your peer" discussions. As well, the design called for a senior TA to lead a weekly review session of the material the students had viewed online.
In the end, I did get the team I had asked for: two relatively senior grad students who could take on a lot of responsibility; two first year grads who would be very helpful with classroom and other course logistics while they learned the ropes; and two student graders. I made one of the senior TAs the "grading czar" and it has been his responsibility to manage all things related to grading, including overseeing the team of graders who are marking the short answer questions on the midterms (the two first year grads + the student graders). The other senior TA was put in charge of the Friday review sessions. I have worked intensively with her on how to prepare a student-centered review that consists primarily of i>clicker and "turn to your peer" instruction. We have also worked on picking out the sorts of details that it will be helpful to emphasize; and how to choreograph and presentation so that it runs smoothly, doesn't have you jumping ahead of yourself, etc.
A ratio of 1 TA/100 students is an absolute minimum for a student-centered, flipped class; better would be 1/50. The students are more engaged and therefore asking more questions; there are more moving pieces and many of these can be handled by TAs (especially after the first iteration of the class). TAs are especially helpful in facilitating peer instruction. In my classroom, because of the design of the room and the fact that there are so few extra seats, I have two of the TAs stand at the doors and help late-arriving students find seats. That has minimized the distraction to me and the rest of the class and prevented students from plopping in the aisles. On exam days, I recruited an extra grad student to help us hand out exams. We put the scantrons into the exam so that we only needed to hand out one item. We then divided and conquered the room. Next time, I will have one person stand at the back and hand exams directly to students who are coming in after we start handing them out. But, using this method, we were able to hand out 400 exams in about 5 minutes and everyone was able to start on time.
I found out on Friday that the TA who was leading the Friday review sections was going to be transferred to another class with discussion sections (a medical emergency had left that course without a TA to do sections). This was not welcome news, but was the best solution for my department as a whole. It now means that I have to take on those review sessions in addition to everything else. This TA did not do grading; but she was slated to grade part of the final exam with me. I am working to ensure that she will be paid an extra stipend to do that. This whole episode reminds me of another mantra associated with teaching, but especially teaching student-centered classes: remain flexible and adaptable at all times.
There was a fair amount of logistical work to do at the start of the course, as I figured out how to divide the different duties among the TAs. Fortunately, I have a fantastic group--reliable and competent in every way. They have been really good at helping me figure out solutions to course logistics and have done what was asked quickly and without complaint. When teaching this sort of a class, especially for the first time, it is essential to have an excellent team of teaching assistants. They are the sine qua non, and it is their contributions that make or break the experience for the students.