The saying ‘You don’t know what you don’t know’ applies to many aspects of life but especially to using technology. In regards to teaching, there can often be an incredible tool with game-changing potential available for our use, if only we knew about it. For mathematics teachers, GeoGebra is one such tool. Most mathematics teachers will have heard of GeoGebra. However, as I have argued in several articles on this site, it appears many math teachers are unaware of the extent of GeoGebra’s power, simplicity and applicability to numerous aspects of middle and high school mathematics. I propose that the number of teachers who utilize GeoGebra (or similar) on a regular basis, at least as a projection tool, to be less than 50%. That is, I’m suggesting less than 50% of mathematics teachers who have access to a computer and data projector utilize GeoGebra as a regular tool, integral to their teaching. How many of the teachers in your department use GeoGebra on a regular basis for their mathematics students? How many don’t? Are you utilizing GeoGebra?