The National Association of Secondary School Principals' Selecting and Developing the 21st Century Principal program is a formative assessment identifying skills linked to effective leadership, and it is based on a simulation designed to replicate a school principal's day. The Long Island School Leadership Center became a site for this program in 2006. Using data generated from a sample of the center's participants, this mixed methods study examined (1) how participants scored on the assessment and to what extent they found it accurate and helpful, (2) the types and levels of professional development follow-up activities participants pursued, and (3) the types and levels of support they received. The findings highlighted that the assessment results proved to be an impetus for action with participants creating a specific plan to further leadership development or by heightening their self-awareness that prompted behavioral changes. The professional development activities of choice were aligned with job-related skills or had the potential to promote advancement, and participants particularly valued ongoing internal administrative support. In a few cases, the combination of identified skills based on assessment performance, coupled with targeted professional development and supported by in-district mentors, accelerated the participant's growth. In this light, this exploratory study forms the basis for further investigations of the nexus of formative assessment, professional development, and support for school administrators.