In this study the author examined the psychometrics of an instrument, the Independent School Teacher Development Inventory, designed to assess the professional learning opportunities in U.S. independent schools. The inventory was sent to 3,422 independent school administrators and of these, 2,474 returned completed surveys. Exploratory factor analysis performed on a randomly assigned half of the sample (n = 1237) suggested that the Independent School Teacher Development Inventory comprises 5 factors: traditional, content, coherence, duration, and active learning/collaboration. Confirmatory factor analysis performed on the second half of the sample provided additional support for a 5-factor structure of the inventory. The Independent School Teacher Development Inventory is a promising tool for assessing professional development practices in independent schools, and further research is warranted to determine whether it may be appropriate for use in public schools. (Contains 4 tables and 2 figures.)