An evaluation system that is designed to support and improve teacher practice--rather than simply to assess and manage teacher performance--would have as its foundation effective and reliable processes to observe classroom practice and give teachers useful feedback. Such an improvement-focused evaluation system should be aligned with and contribute to a district-wide system that includes a shared definition of teacher quality, a clear set of district priorities, and a coherent strategy for improving teacher practice. High-quality observations demand skilled observers who deeply understand a common frame of reference for quality teaching (the rubric their district uses), who reliably interpret classroom evidence according to this rubric, and who give teachers timely feedback that is targeted to improve their practice. The challenge for districts and states now is how to train and support these observers. What types of training and support do observers need, and what is being provided? Does effective training improve observer skills and, ultimately, classroom practice? To address these questions, the authors examined recent research on observer training and explored the training efforts in a sampling of five districts: Boston, Massachusetts; the District of Columbia; Santa Fe, New Mexico; Maricopa County, Arizona; and New Haven, Connecticut. This brief describes key takeaways from their research and from conversations with trainers, researchers, and district officials.