I am a graduate student and have been using TBL for 2 semesters and 2 summer sessions now.  Though I really like TBL, I feel I've struggled a bit with the implementation.  This summer (in a class of 9 students), I finally felt like I "got it".   I tried to make activities more concrete and focused on "telling a story" and making the activities relatable.  However, this semester I will be teaching Biopsychology (behavioral neuroscience and hormones and behavior) for the first time and there are 208 students in the class.  I would really like to use TBL, but I'm quite nervous about it.  

My particular weaknesses seem to be keeping the material accessible and clear and facilitating discussions between groups.  Though I feel I got this in the small class, I'm worried about how this will transfer to a large lecture hall.  I've used TBL in large classes before (last spring I had 17 groups), but it didn't go as well as I'd like, and it was like pulling teeth to get students to engage in discussions with each other (they generally talked to me instead).  Does anyone have any tips they can share about how to foster interactions between groups in such a large class?  This class meets twice a week for an hour and 20 minutes.

Any tips on the logistics of running TBL efficiently in  large lecture classes would be appreciated as well!