Abstract: Learning by doing has proven to be an effective methodology for many years, and learn-by-doing computer simulations have been quite successful. However, physical tasks do not lend themselves well to simulation, yet there is a need in many companies for large-scale, geographically-distributed training on simple physical tasks. In this paper, I describe the Mobile Stocking Training System, a novel learn-by-doing training and performance-support program for a major retailer in which the learner is immersed in a learning environment that mixes PDA-based e-learning with real-life tasks. The learner is taught concepts on the PDA, and then stocks actual shelves in a real store, and uses photos on the PDA to evaluate his performance. This method is immersive, engaging, and provides a cost-effective way to deploy authentic training on a large scale.