The authors’ goal was to improve their online environment by testing and modifying it to support teachers' development of deep, connected understandings of school mathematics and to find ways to make use of the teachers' learning as a context for subsequent mathematical and pedagogical development. The authors propose a model for developing mathematical knowledge for teaching (MKT) in an online environment. The authors believe that their model for Online Asynchronous Collaboration (OAC) is a promising practice in teacher education.