There is a growing awareness that an engineering presence within the K-12 curriculum provides an authentic contextual base for mathematics and science concepts. One large scale initiative focused on pre-college engineering is the National Center for Engineering and Technology Education (NCETE) funded through the National Science Foundations' (NSF) Centers for Learning and Teaching program. One key problem that emerged from a multiple case study project of engineering teacher professional development funded by NCETE was the lack of a well-defined conceptual base for K-12 engineering. The development of meaningful learning, teaching, and assessment is problematic in the absence of a clear understanding of the conceptual base of the subject matter--in this case K-12 engineering. Given the current ambiguity of the conceptual base of secondary engineering, and the need for conceptual clarity in curricula, professional development, and research, this study was designed to coalesce a body of engineering concepts for the secondary level. The purpose of the study was to identify and refine a conceptual base for secondary level engineering education. Operating under an emergent qualitative research design, an adaptive approach to data collection was utilized. Four sets of documents were reviewed and three focus groups were conducted. The outcomes of the study consisted of much more than a list of core engineering concepts and are thus worthy of discussion to shed light both on the researchers' method and in terms of implications. Although not an original purpose of the study, the process used to identify the concepts raised a number of questions and issues important for secondary level engineering education that the researchers felt necessitated discussion. In addition, the peer debriefing participants were asked to reflect on these issues as they were deemed by researchers as being just as important as the list of concepts. (Contains 2 tables.)