How to engage students in oral presentations? Paper-based exams are not fully representative of knowledge, and it is good to consider oral presentations of students as a factor for the final grade to some extent. This is somehow the case in graduate courses, where the number of students is lesser, but how to follow this strategy for crowded classroom of inexperienced undergraduate students. I mean a classroom of 50+ size with students who do not have experience in scientific discussion!
I would like to add to earthling's answer. If you have teaching assistants, please do make good use of them in this aspect. 

As a TA, I have had excellent experiences in mentoring undergraduates to prepare research presentations, final papers, projects and proposals for these papers and project. Of course, we were generally in a class of 120-160 students so that speaks to a classroom scale higher than what you are suggesting. There were 3 graduate TA's, usually and we each had about 50 students to mentor. We found that we could devote significant amounts of time to each student when we met them on a one-on-one basis. Of course, the professor also met them one-on-one and there were a couple of rounds of iteration of their final presentations - which was very, very useful for the professors, the TA's and the students. As mentioned previously, it was a time sink, but very well worth it.