We begin this article by situating a methodology called "developmental maieutics" in the emerging field of mind, brain, and education. Then, we describe aspects of a project in which we collaborated with a group of physical science teachers to design developmentally informed activities and assessments for a unit on energy. Pen-and-paper assessments, called "teasers," were employed, along with interviews, to study how students learned about the physics of energy. Results were used to describe students' learning pathways and to design a scoring rubric for teacher use. We hypothesized that (a) teasers, by themselves, could be used effectively to evaluate the developmental level of students' reasoning about energy and (b) teachers could employ the scoring rubric with minimal instruction. Encouraged by our findings, we went on to create a freely available online version of the "energy teaser," including a new rubric designed to improve the accuracy with which teachers can assess the developmental level of students' energy conceptions.