Teachers' knowledge of mathematics is pivotal to their capacity to provide effective mathematics instruction and to their ability to assess student learning (Ball, Hill, & Bass, 2005; Ma, 1999; Schifter, 1999). The National Council for the Teaching of Mathematics (NCTM, 2000) makes it clear that teachers need knowledge of the whole domain as well as knowledge about the important ideas that are central to their grade level. POWERSOURCE is expected, through professional development and job aids, to influence teachers' pedagogical content knowledge and assessment practices. To gauge such effects the authors have developed teacher measures that focus on three key mathematical principles that are central to POWERSOURCE: the distributive property, solving equations, and rational number equivalence. (Contains 2 figures.)