The Collaborative Development of Expertise (CDE) is an effective, low-cost training methodology for conducting one-on-one training and team training. Preliminary validation results reveal CDE s effectiveness in promoting (1) greater trainee participation during post-exercise debriefs, (2) better match of trainee-instructor prioritizations during a training exercise, and (3) higher trainee scenario performance as compared to a control group. Furthermore, instructors using CDE (1) use a greater breadth of instructional strategies, (2) are more flexible in the strategies used, and (3) are better able to match the right instructional strategies to the type of performance issue. This paper describes the components of CDE, the steps involved, and discusses the learning theory behind these components. CDE provides the instructor and trainee with a step-by-step training methodology, as well as a toolbox of instructional approaches for unpacking the expertise of the instructor. The process begins with the instructor fostering a more collaborative training environment. Next, CDE uses Cognitive Task Analysis to delineate the types of challenges associated with a job. These challenges provide a framework for the instructor and trainee to diagnose training deficiencies together. Instructors further categorize observed performance obstacles as either a knowing, thinking, or doing-related problem. These categories help the instructor to identify whether the problem involves a lack of declarative knowledge, difficulty in decision-making, or whether the trainee is having trouble with the procedures associated with a task. Categorizing problems in this manner serves to further facilitate diagnosis, and provides a basis for choosing an appropriate instructional approach from the many provided to the instructor by CDE. Finally, CDE empowers trainees to use knowledge elicitation approaches to help unpack the instructor s expertise, as ownership of the training belongs to both the instructor and trainee alike when the using the CDE process. Future work in evaluating and refining CDE is proposed.