I'd be curious to hear from other college teachers what kinds of structured activities they've found to work well for philosophy discussion sections (also called 'precepts' here, or 'tutorials' back home in NZ). The default of whole class discussion is fine as far as it goes, but tends to lead to very imbalanced participation. Occasionally splitting the class up into small groups can help with this, though their assigned task needs to be very clearly defined or there's a risk that they'll just sit there and not know what to do. Let me describe a structure that I found worked really well for my applied ethics class this year -- then I hope others will chip in with their own suggestions.
Firstly, the grading schedule for the class required each student to give a 'precept oral presentation' at some point, worth 10% of their grade. Unfortunately, students tended to just summarize the assigned readings, rather than critically engaging with them in any depth. But one thing that helped with this was that I asked the presenting student each week to come up with three central questions (based on the readings) for the rest of the class to discuss. This helped a bit, though in most cases the critical questions were just "tacked on" to the end of the summary presentation, rather than re-shaping it as I'd hoped. (I'd really welcome any suggestions from more experienced teachers about how to get students to give better -- more critically engaged -- presentations.)
Anyway, with the presenting student's three proposed questions on the table, I'd then split the 12-person class into three small groups, and assign them one question each to discuss. (Sometimes I'd step in to elaborate on or add to some of the questions if it seemed necessary, to help the students to get a sense of how it might be tackled.) I suspect this wouldn't always work, but I had good students and accessible topics, so they tended to have very vigorous discussions amongst themselves for the assigned 5 - 10 minutes. We'd then reconvene, and spend the rest of the precept addressing the three issues in turn, beginning with a spokesperson from the relevant small group summarizing their discussion, and then opening it up for a wider class discussion.
So, I found that this worked pretty well, at least in the context of an applied ethics course. But I'd be curious to hear others' suggestions. (Has anyone tried running in-class "debates", for example?)