The important consideration is whether or not the time is well spent. That' s a disappointing fact that we all face at one time or another. But it's not really so surprising that students don't participate if we consider the little experience they may have had with the method. Discussion requires student skills as well as teacher skills. They must be able to state ideas or feelings clearly, to summarize, to analyze, to clarify, to accept others' disagreements, to derive generalizations, etc.
Discussions always get better as the semester goes along .
Students will be more inclined to participate when they see what the discussion is all about. Patience and encouragement on your part may wear away this barrier to good discussions.