In this study we document how a mathematical idea, shared by a student, changes the development of the class discussion. Our work characterizes the flexible and open dynamics in mathematics instruction that a teacher adopts to give her students control of their own mathematical ideas. Our work argues that this flexibility is necessary for teachers to engage in instructional practices that respond to students' mathematical thinking. To demonstrate the teacher's flexibility we use the analogy of soccer, relying on the literature of Game Sense coaching approach, which suggests that the coach (the teacher in our context) is positioned to manipulate the practice environment with the purpose of facilitating learning. [This paper is provided in both Spanish and English. For the complete proceedings, see ED606556.]