This article describes the development and validation of two forms of the Geometry Assessments for Secondary Teachers (GAST), which were designed to assess teachers' knowledge for teaching geometry. Both forms were developed by teams of mathematicians, mathematics educators, psychometricians, and secondary classroom geometry teachers. Predictive validity for the GAST assessment was explored by observing and testing 157 teachers as well as administering pre– and post–tests to 3,698 students. The reliability coefficient for both GAST assessment forms was acceptable (r = .79). GAST assessment scores explained a statistically significant but small amount of the variance of student scores, demonstrating an effect that was greater than the number of years of teaching experience but smaller than the effect of having an advanced degree.
Margaret Mohr-Schroeder, University of Kentucky, Department of STEM Education, 105 Taylor Education Building, Lexington, KY 40506-0001; email@example.com
Robert N. Ronau, Emeritus, University of Louisville; National Science Foundation, Arlington, VA 22230; firstname.lastname@example.org
Susan Peters, University of Louisville, Department of Middle and Secondary Education, Louisville, KY 40292; email@example.com
Carl W. Lee, University of Kentucky, Department of Mathematics, 715 Patterson Office Tower, Lexington, KY 40506-0027; firstname.lastname@example.org