Research and development of Learning Analytics (LA) have created new ways to support students' learning. However, our understanding of teachers' roles when implementing LA in classroom practices remains nascent. This study investigates how teachers can implement LA to support students' agency in directing their own inquiry, when engaging in a digital pedagogy approach known as Knowledge Building (KB) on an online platform called Knowledge Forum (KF). Together with a teacher experienced in KB and KF, we co-constructed interventions anchored on two easy-to-use LA tools in KF, the Scaffold Tracker and Word Cloud. These LA interventions were enacted with a Grade 5 class of 18 students and another Grade 6 class of 18 students. Three teacher roles were identified: detecting behaviour unproductive to collaboration, mediating between LA and student self-assessment, and framing student-generated lines of inquiry in actionable ways. We coded KF notes for the discourse moves they reflected and found that after the teacher implemented the LA interventions, notes that sustained inquiry increased sharply with students' focus shifting from individual to collective knowledge and from superficial explanations to deep understandings. We discuss the implications of these findings on the development of ways to bridge LA research and practice.