Randall Eberts explores the role of teachers unions in public education. He focuses particularly on how collective bargaining agreements shape the delivery of educational services, how unions affect both student achievement and the cost of providing quality education, and how they support educational reform efforts. Eberts's synthesis of the empirical research concludes that union bargaining raises teachers' compensation, improves their working conditions, and enhances their employment security--while also raising the cost of providing public education by upwards of 15 percent. The effect of unions on student performance is mixed. Students of average ability who attend school in union districts perform better on standardized tests, whereas low-achieving and high-achieving students perform worse. However, the overall gain in achievement does not make up for the higher cost. Of late, unions have begun to be more supportive of school reform, moving from an adversarial bargaining model to a more collaborative one in which teachers and administrators share common goals and hold joint responsibility. Yet unions' desire to participate in reform does not match their fervor to organize in the 1960s and 1970s. While national union leadership has talked about reform, local affiliates have initiated most of the reform efforts, pioneering reforms such as accountability and incentive pay. In Eberts's view, one reason that unions have been slow to embrace reform efforts is the lack of consensus on their effectiveness. He argues that many reforms have been too narrowly focused; rather, effective schools result from well-designed systems and processes. In principle, adopting standards that help teachers focus on lessons they want students to learn, aligning their teaching to the lessons, and devising measurements that demonstrate that students are responding to these lessons can improve teaching as long as the public, policymakers, and school administrators acknowledge the complexity of the learning process and the broad outcomes that society desires. (Contains 69 notes.)