Group-level metacognitive scaffolding is critical for productive knowledge building. However, previous research mainly focuses on the individual-level metacognitive scaffoldings in helping learners improve knowledge building, and little effort has been made to develop group-level metacognitive scaffolding (GMS) for knowledge building. This research designed three group-level metacognitive scaffoldings of general, task-oriented, and idea-oriented scaffoldings to facilitate in-service teachers' knowledge building in small groups. A mixed method is used to examine the effects of the GMSs on groups' knowledge building processes, performances, and perceptions. Results indicate a complication of the effects of GMSs on knowledge building. The idea-oriented scaffolding has potential to facilitate question-asking and perspective-proposing inquiry through peer interactions; the general scaffolding does not necessarily lessen teachers' idea-centered explanation and elaboration on the individual level; the task-oriented scaffolding has the worst effect. Pedagogical and research implications are discussed to foster knowledge building with the support of GMSs.