The Performance Assessment System (PAS) is a portfolio assessment mechanism used to evaluate beginning teacher performance as a function of the teacher's approach and effectiveness at increasing student learning and growth. The PAS was originally developed by Teach For America, the national teacher corps, as an internal assessment tool for its teachers. The PAS has evolved in response to input from participants, administrators, and external evaluations over the course of four pilot implementations. Specifically, developers have streamlined requirements, focused efforts to incorporate measures of student performance, and clarified scoring rubrics. The PAS continues to be piloted as an assessment resource that eventually will help districts to retain only beginning teachers who are effective in the classroom and will empower states to license only teachers whose performance meets approved standards.