Background: In the last decade, the effects of teachers on student performance (typically manifested as state-wide standardized tests) have been re-examined using statistical models that are known as value-added models. These statistical models aim to compute the unique contribution of the teachers in promoting student achievement gains from grade to grade, net of student background and prior ability. Value-added models are widely used nowadays and they are used by some states to rank teachers. These models are used to measure teacher performance or effectiveness (via student achievement gains), with the ultimate objective of rewarding or penalizing teachers. Such practices have resulted in a large amount of controversy in the education community about the role of value-added models in the process of making important decisions about teachers such as salary increases, promotion, or termination of employment. Purpose: The purpose of this paper is to review the effects teachers have on student achievement, with an emphasis on value-added models. The paper also discusses whether value-added models are appropriately used as a sole indicator in evaluating teachers' performance and making critical decisions about teachers' futures in the profession. Research Design: This is a narrative review of the literature on teacher effects that includes evidence about the stability of teacher effects using value-added models. Conclusions: More comprehensive systems for teacher evaluation are needed. We need more research on value-added models and more work on evaluating value-added models. The strengths and weaknesses of these models should be clearly described. We also need much more empirical evidence with respect to the reliability and the stability of value-added measures across different states. The findings thus far do not seem robust and conclusive enough to warrant decisions about raises, tenure, or termination of employment. In other words, it is unclear that the value-added measures that inform the accountability system are adequate. It is not obvious that we are better equipped now to make such important decisions about teachers than we were 35 years ago. Good et al. have argued that we need well-thought-out and well-developed criteria that guide accountability decisions. Perhaps such criteria should be standardized across school districts and states. That would ensure that empirical evidence across different states is comparable and would help determine whether findings converge or diverge.