Certain aspects of theoretical frameworks in mathematics education can remain unexplained in the literature, hence unnoticed by the readers. It is thus interesting to participate in a dialogue where they can be discussed and compared in terms of the aims, objects studied, results and their relation to teaching. This study is focused on how APOS Theory is used in research and how it can be useful to instructors. An example of its application in the context of a Linear Algebra problem is given, followed by a discussion about how insights about students' understanding can guide teachers' activities in the classroom.