Perhaps through cooperative learning? You could give students specific jobs within each group that give them some kind of responsibility over the group's activities as a whole.
We have a Leadership Club for grades 5-8. They work on planning and running student-led assemblies once a month. We also have Leadership Lunches once a month where we bring in an outside speaker who has a pizza lunch with a small group (12) of students who sign up for the lunch. This is new this year, but seems to be popular. The idea is for the students to hear from someone who is a leader - in any way or path of life. We are trying to promote a culture of every student is a leader. We sent three teachers to a Leadership conference at National Cathedral School last May; they came back with some great ideas.