Studies analyzing explanations that have been constructed by science students have found that they were generally weak and lack necessary features. The goal of this study was to establish the competencies that one needs to construct a scientific explanation. Scientific explanations can be looked at in three ways, in terms of their function, form and level, as being essentially sign-making processes. Taking a case study approach and using Lemke's multimodal framework, we analyzed the scientific explanation of an electromagnetic induction phenomenon constructed by one high school student. We found that such a construction involves the complex coordination of different types of signs, not only to represent the entities in the phenomenon, but also to support thinking and reasoning about it at abstract levels. Scientific conventions and rules, and everyday material and social tools were found to be crucial in shifting from one level of abstraction to another. The findings highlight the importance of developing the skillful use of schemes of scientific representation by students and familiarizing them with commonly encountered contexts.