The scholarship on teaching and learning shows that students learn better when they actively participate in the learning process than when they passively receive information. One of the most basic and accessible active learning techniques is the class discussion. Many teaching assistants are assigned to lead section meetings that may even be called "discussion sections." The small-group format (or, at least smaller than the lecture) is supposed to give students a chance to ask questions in a more comfortable environment and to discuss the material. Some TAs use the time to give a lecture or review the reading material, particularly if the professor doesn't directly address the reading in his or her lectures. If section meetings mainly recapitulate the reading material, they may become a waste of time for students who have done the reading, or a way for students to avoid reading, since the TA will tell them what they need to know. The section meeting can be a place for students to directly engage with the ideas. Discussions can give students a chance to formulate arguments, think through problems, make connections among concepts, start to see how concepts apply to other contexts, and respond to other people's points of view.
Good discussions require preparation and planning; you need to have questions and strategies in mind, and be ready to shift to a new line of questioning if one set of issues is exhausted more quickly than you expected. To get a productive discussion going, you need to ask the right kinds of questions. Some instructors start with a very general question, like, "So what did you think of today's reading?" This may elicit responses, especially if you have one or two talkative students who are just waiting for an invitation to speak, but many students won't know how to respond to such a broad question. Try to ask questions that are open-ended—they don't aim at a single correct answer—but are specific enough that students have a way into the material. Ask "why" and "how" questions rather than ones which allow a "yes" or "no" answer. A few things you can ask students to do are: focus on one particular aspect of the material; link a specific text or issue with another specific text or issue; argue for or against one point of view; think about how an idea would apply in another context; and give real-world examples of concepts. You can also ask students to share what they learned from a text or lecture, what they thought the most important new idea was, whether anything surprised them, or what image or example was most memorable. See what themes emerge from their answers.
After posing a question, give students some time to think about their responses. Instructors often fear the discomfort of silence, and rush to fill it if students don't start answering right away. Instead of offering your own answer or moving on to another question, wait a few minutes. Even if one student immediately raises his or her hand, you may still want to wait a bit before calling on that student, to let students know they'll have time to formulate a response. You can also have students write for a minute or two, and then ask them to share their answers. This way, everyone will have to think through the question, and shy students may feel more comfortable speaking up if they can read their answers. Another way to prepare students for a class-wide discussion is to first break them up into small groups or pairs that will discuss a specific problem or issue and then report back to the class.
Your role as the discussion leader is to keep students focused and on track; if students get far off topic, remind them what the task at hand is. Follow up on student responses by asking for specifics or evidence or elaboration of a point, and encourage students to respond to or extend each other's answers. It is not necessary to comment on every contribution to the discussion; you'll end up talking too much and dominating the class. If you have to correct a wrong answer or incorrect information, do so gently, and try to point out what was right about the student's answer. Letting a few students do all the talking while most of the class remains silent makes things easier for the instructor, but you need to try to involve as many students as possible in the discussion. Call on students who haven't participated before when they do raise their hands, and every once in a while ask to hear from students who haven't yet contributed. Another important task is to make sure that the discussion remains civil and respectful, even if it becomes heated. Set out guidelines that make it clear that students must respect each other, even when they disagree, that they may (and are encouraged to) challenge each other's and the instructor's ideas, but they may not attack anyone personally, insult them, or call them names, and that students shouldn't interrupt or speak over each other.
Leave a few minutes at the end of class to summarize the discussion and perhaps to point out how the issues you've covered that day connect to the material from the previous class and lead into future topics. Show students that they've progressed through a series of issues and that the class has accomplished something.