This article draws on M. M. Bakhtin's (1981) notion of dialogism to articulate what it means to understand a scientific idea. In science, understanding an idea is both conceptual and epistemic and is exhibited by an ability to use it in explanation and argumentation. Some distillation of these activities implies that dialogic understanding of a scientific idea includes being able to use it to explain natural phenomena, being aware that it is one among a multiplicity of alternatives, and that the scientific idea is superior to alternatives based upon a scientific evaluation which involves relating it to evidence. This notion of dialogic understanding is related here to a scaffolding framework, which we argue characterizes one form of instructional support for framing content dialogically as part of explanation and argumentation. For illustration, the framework is applied to data from a high school evolutionary biology course. In contrast to the prevailing position that dialogic understanding should be supported through engaging in argumentation (i.e., actual dialogue), we entertain an additional possibility that dialogic understanding can be supported through dialogic framing. We also entertain the possibility that dialogic framing of content can provide initial support for student engagement in argumentation. (Contains 3 figures and 1 table.)