Peer review of teachers is controversial for several reasons. Some say peer reviewers encroach on the rightful domain of the principal as instructional leader. Others argue that, because peer evaluators are fellow teachers, they may be biased or unwilling to make hard decisions. Many teachers find the prospect of peer evaluation unsettling because it violates the professional norm of egalitarianism--the assumption that "we're all equal." Some traditional teacher unionists reject peer review as a plan that sets teachers against one another. Now that districts across the United States are rushing to implement new evaluation systems, many are taking a new look at peer review. They have good reason to do so. Peer evaluators can reduce the demand on administrators' scarce time, provide subject-matter expertise that a principal may lack, introduce the teacher's perspective into the evaluation process, and enable teachers to take greater control of their profession. Does peer review have the potential to be used widely and to improve teacher evaluation? Or is it too problematic to succeed and last? A look at seven districts' Peer Assistance and Review programs shows what it takes for this approach to succeed. The experiences of these districts suggest that peer review can work well if key components are in place: open and rigorous selection, clear performance guidelines, explicit instructional standards, ongoing training, and effective supervision. (Contains 1 endnote.)