Increasingly content area projects and programs at the K-12 level, such as in mathematics, involve a programmatic component or project emphasis on developing "teacher leadership". However, there is no consistent definition or framework for this construct and even fewer validated tools for measuring it. This paper describes our efforts in developing such a framework, constructing a situational judgment test instrument for measuring it, and validating the instrument. The developed instrument shows promise in being able to reliability measure constructs associated with the concept of teacher leadership in mathematics though more work needs to be done.