The Vermont portfolio assessment program has had substantial positive effects on fourth-grade teachers' perceptions and practices in mathematics: Teachers report that they have learned that mathematics is more than computation, and they regularly teach problem-solving skills. However, teachers have had difficulty understanding certain key aspects of the reform. They do not share a common understanding of mathematical problem-solving and do not agree on problem-solving skills. As a result, they tend to focus on the scoring rubrics to guide student efforts. Without common understanding among teachers and adequate controls on student preparation and administrative conditions, scores from non-standardized, instruction-embedded assessments may not support proposed uses involving comparisons among students, classrooms, schools, or systems. Vermont should continue its efforts to expand the knowledge of its teachers and to supply them with additional materials to guide pedagogy and classroom activities.