As part of Washington State's efforts to ensure and improve the quality of the teacher workforce, the Professional Educator Standards Board (PESB), with assistance from Educational Testing Services (ETS), has recently introduced a new, evidence-based assessment of teachers called the ProTeach Portfolio. The development of ProTeach was mandated by the Washington State Legislature in 2007. Specifically, PESB was charged with the task of developing and implementing a uniform assessment that demonstrates teachers' knowledge and skills for producing a positive impact on students' learning. The ProTeach assessment, a key component of the state certification program, seeks both to recognize a high level of achievement in the profession and to "prepare educators who are able to assess their professional growth and achievement in light of their impact on student learning" (Washington Administrative Code, x181-79A-007, 2012). The Center for Education Data and Research (CEDR) at the University of Washington Bothell has been contracted by PESB to analyze the ProTeach assessment and its alignment with student academic achievement on the Washington Assessment of Student Learning (WASL). PESB asked CEDR to answer four questions: (1) Does the proposed ProTeach pass/fail cutline identify teachers who are less effective as measured by student achievement? (2) How much, if any, of the variation in student achievement attributable to teachers is accounted for in the ProTeach composite score? (3) How well do the twelve subcategories of the assessment capture variation in student achievement? and (4) Does classroom composition affect teacher performance on the ProTeach assessment? Study data and analytic approach, ProTeach portfolio results and teacher effectiveness, assessment of alternative ProTeach procedures, and policy implications are detailed in the report. Appendices include: (1) Analytic Models; and (2) Additional Empirical Results.