Scholars and practitioners have long criticized teacher evaluation as ineffective. Peer assistance and review (PAR) alters traditional teacher evaluation, as master teachers conduct summative as well as formative assessment of beginning teachers and veteran teachers in need of intervention. Relying on data from a longitudinal case study of one urban district, this article describes key components of teacher evaluation with PAR, in particular how it differs from teacher evaluation as typically conducted by principals. Findings are reported across six key factors: time, professional development, transparency, labor relations, decision making, and accountability. Notably, a substantially higher level of accountability appeared present with PAR than prior to program implementation. In contrast to popular opinion, this study provides an example of teachers willing and able to engage in the summative evaluation of their peers, a key component of professionalism and professionalization. Implementation challenges and areas for future research are addressed.