This study investigates the effective research-based characteristics of professional development (ERBCPD) of the National Science Foundation's GK-12 Program--a program which partners institutions of higher education with local school districts and places science, technology, engineering, and mathematics graduates in the K-12 classroom with teachers. Final evaluations of 26 GK-12 sites were analyzed with a priori and emergent content analyses, which included rigorous inter- and intra-reliability testing. The results of the a priori analysis demonstrated that the GK-12 program incorporates all ERBCPD, but to drastically varying degrees (76-5%). The a priori characteristics that appeared most often were "Treats Fellows as professionals," and "Professional development is on-going." The two emergent characteristics included "Improves communication skills" and "Has real world application."