We present results of the analysis of knowledge used by a secondary school mathematics teacher in her classroom practice. This knowledge takes shape and is displayed as specific teaching strategies in the management of her class when she incorporates Computer Algebra Systems. Based on observations of regular classes, we find that her knowledge (mathematical, pedagogical and technological) is put into action at various moments during the lesson and through a variety of teaching strategies. These strategies depend on many factors, such as the planned objective of the lesson, the specific moment in the class, student participation, and the use of technological tools. Within such complexity, the teacher applies her teaching strategies in a flexible way, and manages to control and even modify the course of her class. [This paper is written in both Spanish and English. For complete proceedings, see ED581294.]