Undergraduate not doing homework (case method)
I have some experience with lab practice in physics and chemistry, where we routinely ask students to read up on the work planned and do some preliminary calculations before they can come to the lab, in order to maximize their use of actual lab equipment. It's sometimes hard to motivate students for things that should be done in advance, but there are ways you can improve their involvement:


Make sure that the amount of material is compatible with the time they have to study it, and the demands on their time by other courses. If you're going to require something of them, it should be within reasonable limits. Also, make sure you convey that point to them: I have, on a few occasions, had to reschedule things to give them more time, because the material was very heavy and taking more of their time than I had assumed, or because they just had many other things to do (e.g., a full week of exams).
Be crystal clear that reading the material before classroom is actually one of the requirements of the class, and that it is entirely necessary to actually pass the class.
If you want further motivation, introduce some sort of evaluation of their reading at the beginning of the lecture: get two or three students to come up, and argue the case (or whatever it is you do in those lectures) before the others. Then, give them a frank assessment of how they fared, including “you failed miserably because you didn't do your homework”. Even if that evaluation doesn't count for the final passing/failing grade, it will motivate them and might introduce some friendly competition.
If some of them still don't do a thing, fail them. After all, you had told them (and more than once) that reading the material is a requirement for passing.