Teachers are the most important school-related factor for student achievement gains, but evaluation of teacher performance is seldom conducted in any rigorous way. As policymakers call for a better approach to teacher evaluation, the 10-year history of TAP[TM]: The System for Teacher and Student Advancement provides an example of an integrated system for teacher evaluation and support. TAP teachers are evaluated every year through multiple classroom observations by trained and certified raters and through their contributions to student achievement growth. Based on data from TAP schools, research shows that: (1) TAP teacher evaluations provide differentiated feedback on teacher performance; (2) TAP classroom evaluations are aligned with value-added student achievement outcomes; (3) TAP teachers become more effective over time; and (4) TAP schools show higher retention of more effective teachers, and higher turnover of less effective teachers. Creating the capacity for evaluation and evaluation-guided improvement in schools requires the right tools as well as the sustained engagement of teachers and leaders. The example of TAP implies that teacher evaluation should not be pursued as a one-time, one-size-fits-all policy prescription, but should be integrated within a comprehensive, site-based system with specific practical elements to support teachers and improve teaching and learning in the classroom. (Contains 7 figures and 5 footnotes.) [For "A Teacher Evaluation System That Works. Working Paper," see ED533380.]