This study describes the development of two instruments, the Principles of Scientific Inquiry- Teacher (PSI-T) and the Principles of Scientific Inquiry-Student (PSI-S), to investigate the extent to which students are engaged in scientific inquiry. As a result of the instrument development process employed, each finalized instrument consisted of 20-items separated into five categories. Based on the analyses completed, the instruments appear to be useful instruments for use in comprehensive assessment packages for assessing the extent to which students are experiencing inquiry in science classrooms.