In order to promote the design of innovative instructional activities at the Linear Algebra, we perform a design-based research project to explore how to teach Linear Algebra at the university level. In this article, we present the results of three cycles of a teaching experiment that we carried out to design, try out, and improve a local instruction theory (LIT) on the teaching of the concepts of spanning set and span in Linear Algebra with first-year engineering students. In a retrospective analysis, we looked for patterns in the data set of all the experiments, and we identified key learning moment of the students. Based on these patterns, we formulated a LIT to support the construction of the concepts of spanning set and span.