The role of the facilitator has become almost synonymously associated with student-centered approaches. However, how a teacher functions as a facilitator is less well defined. This article begins to define teacher action in student-centered learning environments. Through an exploration of teacher behavior, teacher--student interactions, and discussions around teacher-as-activator, the article argues that the teacher must play an active role in the classroom and should be considered much more than a "guide on the side." Teachers should use a range of direct and indirect behaviors and dialogical exchanges to support and extend learning. These actions and interactions should be contextually relevant and aligned with the learning aims of the student-centered approach. In suggesting that facilitation provides a narrow perspective on teacher action, the article calls for further consideration around teacher-as-activator to consider the teacher as someone who activates new learning possibilities.