Research over past decades consistently shows that traditional pre-service teacher preparation programs are not adequately preparing beginning teachers for the reality of classrooms. The purpose of this paper is threefold. We describe the development of an online classroom simulation, the specific design features in our initial prototype version of the software and our research into our first trial of this with pre-service teachers. The classroom simulation allows the user to take on the role of the teacher of a virtual Kindergarten classroom, working with students aged 5 to 6 years of age. During the simulation the user is required to make decisions about the organization of teaching and learning experiences, classroom management, and responses to individual students. The user is able to monitor and track the progress of three targeted students throughout the course of the simulation. An embedded tool, what we refer to as the "thinking space", has been developed to enable the user to plan and justify new decisions and reflect upon the consequences of previous decisions.