This article describes how a teacher orchestrated a productive mathematics discussion to draw out mathematical knowledge and connect different areas of mathematics following a geometric sequences task. Whenever teachers succeed to engage their students in producing mathematics, it is advantageous for their moves to be analysed, discerned and imitated. The main purpose of this article is to present the moves of a specific mathematics teacher while implementing a rich task and supporting students through the process of making sense and having this process become visible. It describes a 90-minute session with future mathematics teachers. They are accustomed working in small groups and to using the whiteboards around the room. The instructor believes that future teachers need to engage in rich mathematical discussions in order to be able to use this strategy on their own.