good question! I have taught for many years as an assistant instructor at my home dojo. We have a pretty defined set of classes that we teach, when teaching a basics class (we work mainly on body movement, and sometimes on breaking down one specific technique). Typically I would come into class with an idea that I want to work on, but sometimes the class makeup is such that doing what I had planned would just not be appropriate. Some flexibility therefore is necessary.
In another couple of weeks I'll officially have my own dojo/club, and I am trying to figure out what kind of teaching plan I want to implement in terms of what to work on first, etc. Of course, this will also have to be flexible, depending on who shows up and what their ability is. Personally I think that teaching has to be fluid and sensitive to all that are involved in the class. Rigidity in teaching would just spell disaster.
All this said, I feel that the class layout is the teachers responsibility, as is the coherency of the flow of techniques.
just my $.02.
All the best,