"Scaleability" is the concept of dramatically increasing, or scaling up, the number of simulated vehicles (and other "entities"), human participants, and geographically dispersed sites involved in a Distributed Interactive Simulation (DIS). ARPA is developing a scaleability toolset which will allow the development and evaluation of DIS exercise scenarios, scaling and network algorithms and techniques, and network topologies in a simulation environment with the goal of developing solutions to the DIS scaling problem. In addition to giving an overview of the architecture and capabilities of the scaleability toolset, this paper presents an example of, and representative results from, employing the toolset to characterize a specific promising scaling technique, the grid-based geographic filtering algorithm.