With inquiry being one of the central tenets of the national and most state standards, it is imperative that we have a solid means to measure the quality of inquiry-based instruction being led in classrooms. Many instruments are available and used for this purpose, but many are either invalid or too global. This study sought to compare two observational protocols: Electronic Quality of Inquiry Protocol (EQUIP) and Reformed Teacher Observation Protocol (RTOP) with regard to reliability, validity, and utility associated with inquiry-based instruction. Analyses included studying item reliability, inter-rater reliability, factor analysis, correlation, and multiple regression of protocol items within the instruments and between the instruments. General findings suggest that both instruments have high item reliability and are effective measures in both math and science classrooms; EQUIP showed higher inter-rater reliability and seems to be more valid for measuring inquiry-based instruction, while RTOP seems better suited for looking more globally at constructivist teaching practices. Additionally, the utility of EQUIP seems to be larger. It is useful for looking formatively at individual teaching practice, as well as studying summative teacher growth or program effectiveness. Further, because EQUIP uses a descriptive rubric instead of a Likert scale, the instrument provides immediate and targeted feedback to teachers, instructional leaders, and professional development facilitators. This feedback includes both a micro view (individual indicators) and a macro view (construct) of teaching practice.