This article responds to calls that have been made for research into how teachers incorporate new assessment ideas into their practice. We draw on a large-scale study that examined the implementation of reform in mathematics in grades 7-10 in Ontario, Canada. We present teacher questionnaire data, and focus on data gathered from case studies for details of what new assessment practices look like in classrooms. We show teachers using a variety of forms of assessment and using assessment to improve student learning. Observed assessment practices went beyond tests to include the use of journals, observation, questioning, self-assessment and unique forms of "quizzes". These practices allowed teachers to examine students' mathematical thinking and provided feedback to students and teachers to improve student learning. We also observed the important role of collaboration, coherence, and the teachers' beliefs in supporting new assessment practices. (Contains 1 table.)