While problem-based learning (PBL) has a relatively long history of successful use in medical and pre-professional schools, it has yet to be widely adopted by K--12 teachers. This may be due, in part, to the numerous challenges teachers experience when implementing PBL. In this paper, we describe specific hurdles that teachers are likely to encounter during the implementation process and provide specific suggestions for supporting teachers' classroom efforts. Implementation challenges relate to 1) creating a culture of collaboration and interdependence, 2) adjusting to changing roles, and 3) scaffolding student learning and performance. By supporting teachers' initial and ongoing efforts, we anticipate that more teachers will recognize the potential of PBL as an effective instructional approach for developing learners who are flexible thinkers and successful problem solvers.