This paper describes a study aimed to identify most common impediments related to the introduction of an open-source mathematical software package GeoGebra. We report on the analysis of data collected during a three-week professional development programme organised for middle and high school teachers in Florida. The study identified challenges participants face during workshops and evaluated the difficulty levels of GeoGebra tools. Findings of the study, complexity criteria of software tools and commonly occurring difficulties, provided the basis for the development of several new materials assisting workshop activities and contributed to the improvement of introductory GeoGebra workshops. (Contains 1 table, 2 figures, 3 online resources and 1 note.)