This paper reviews a year's work with third-grade teachers who introduced performance assessments in the hope of improving both instruction and assessment in mathematics. The 14 participating teachers in 3 schools tried many changes in their educational and assessment practices. Patterns of stability and change that resulted from their efforts were examined, focusing in-depth on six teachers. The main finding was that the teachers indeed adopted many changes with respect to course content and pedagogy and assessment. Changes in assessment and instruction were mutually reinforcing for most of the teachers. By the end of the year, many were using more hands-on and problem-based activities that were closely aligned with the "Standards" of the National Council of Teachers of Mathematics. The introduction of performance assessment raised teachers' expectations of what their students could accomplish. Change resulted, not from what teachers were told to do, but from what they experienced as they attempted to change. An appendix provides examples of math tasks provided by the project. (Contains 2 figures, 1 table, and 21 references.) (SLD)