There is a clear call in group counseling practice and training for evidence-based practice (ACA, 2005; ASGW, 2008; CACREP, 2009). At the same time, group counselors also are asked to keep clients' experience at the center of their work (ASGW, 2012). This article outlines the authors' effort to develop and study an instrument designed to measure group counselors' conceptualization skill using group members' subjective perceptions as a foundation. Descriptions of the instrument's internal reliability, construct validity, and generalizability will be presented, as well as suggestions for conducting research on this instrument in future studies. (Contains 3 tables and 2 figures.)