Abstract
The article presents a part of design experiment aimed at devising a way to develop Specific Skills needed to work with GeoGebra in future mathematics teachers. The focus is on the skill to interpret numerical results.
The research questions are: Are future teachers aware of the way GeoGebra works with irrational numbers? Do they interpret numerical results when solving and posing tasks in GeoGebra? Are they able to recognise decimal expansions of common rational and irrational numbers? The data consist of solutions to a carefully devised worksheet tasks and proposals for teaching with the help of dynamic geometry. The data were analysed in a qualitative way.
A substantial number of preservice teachers do not use the skill to interpret numerical results properly. Examples of such (mis)use are provided as well as possible causes for the lack of attention to the interpretation of numerical results and pedagogical implications.