Information and Communication Technologies (ICTs) can provide rich learning opportunities in classroom teaching, which requires teachers’ effective instrumental orchestrations. However, there is a lack of research regarding the development of teachers’ instrumental orchestrations. In this study, we designed and implemented a professional development course, aiming to explore whether the course could change preservice mathematics teachers’ instrumental orchestrations. To this end, an analytical framework of instrumental orchestrations within a GeoGebra environment was established. Data were collected from Chinese preservice mathematics teachers, including the videotapes of their simulated lessons, GeoGebra files, written documents, self-reflections, online speaking, etc. In the results, three participants’ changes in instrumental orchestrations were presented as main cases. It was found that the three preservice mathematics teachers’ types of instrumental orchestrations did not change, but the frequencies of those increased significantly. The changes in didactical configurations were mainly reflected in the layout of GeoGebra, and the changes in exploitation modes were mainly manifested in the techniques teachers use and the management of mathematics tasks. In addition, it was revealed that theoretical support (instrumental approach), technical support (knowledge about using GeoGebra), and community support (“Same Content Different Designs” activity and communicating and discussing with others) were useful course elements inviting changes in instrumental orchestrations. In this regard, this study contributes to providing a promising professional development course that can be used in teacher training so as to improve teachers’ instrumental orchestrations.