This paper discusses the use of simulations in the professional development of school leaders. It compares two National Association of Secondary School Principal (NASSP) programs: the "Springfield Development Program" and the "21st Century School Administrator Skills Program" (SAS) and identifies the characteristics of SAS that are aligned with the Interstate School Leaders Licensure Consortium (ISLLC) Standards. The "Springfield" program was created as a training and development program for assessment-center participants who showed high potential to be effective school leaders. This approach worked well when the number of applicants for school leadership positions exceeded vacant positions. Now that there is a shortage of qualified applicants, a new simulation model is needed, and the SAS program builds on and refines the strengths of the "Springfield" approach. The original "Springfield" skills have been increased to eight, and these skill dimensions are aligned with the ISLLC Standards and the new NASSP Assessment Center Skills. Three skill dimensions remain the same: judgment, organizational ability, and sensitivity. The five new skills are oral communication, organizational ability, results orientation, setting leadership direction, teamwork/team leadership, and written communication. Other refinements to "Springfield," such as on-the-job feedback and simplified participant data, are discussed. (RJM)