The National Science Teachers Association (NSTA) recently launched a comprehensive electronic professional development (e-PD) online portal, the NSTA Learning Center. This support site for educators currently includes over 6,000 e-PD resources and opportunities available on-demand, as well as various tools designed to help educators maximize the effectiveness of using NSTA resources. One tool, the PD Indexer, helps teachers identify their own areas of content strengths and weaknesses by selecting content-specific assessments. Individual NSTA resources are recommended based on assessment outcomes. This paper presents a detailed description of the procedures employed by NSTA to develop valid and reliable PD Indexer content-specific multiple-choice assessment items.