Frontline museum floor staff people are critical agents in the field's efforts to catalyze greater community engagement and participation at the intersections of science, art, history, and society. Yet, coming from widely disparate backgrounds and often with little formal professional development in place, many museum-based education practices are informed still by classroom-based (transmission or instructionism) models of teaching and learning. Such approaches may limit the reach and impact of our work, particularly with respect to communities that are under-represented in museum audiences. Drawing on their respective experiences leading science museum professional development programs in the US and the EU, the authors review key ideas from research in the learning sciences that, combined with the educator professional development literature, challenge some of the deep-seated epistemological conceptualizations embodied in practices of many museum educators and suggest the need for new approaches to professional development for museum educators. (Contains 12 notes.)