Authentic Argumentation With Prospective Secondary Teachers: The Case of 0.999…

Engaging prospective secondary teachers in mathematical argumentation is important so that they can learn to engage their own students in creating and critiquing arguments. Often, when we attempt to engage prospective secondary teachers in argumentation around topics from secondary mathematics classes, the argumentation is not authentic, as they believe they already know the answers. There are problems related to the secondary curriculum around which students can be engaged in authentic argumentation, one of them is whether 0.999… = 1.