Educational policy research on teacher unionization in the United States has been dominated by two theoretical perspectives: "rent-seeking" and "teacher voice." While bringing valuable insights to bear, these views have mutated into rigid and often ideologically charged alternatives with strong normative claims about teacher collective bargaining. Drawing from a political economy framework, this article advances a distinct theoretical perspective focusing on the "progressive coalition building" activities of teachers' unions (i.e., organizing and mobilizing to promote the interests of working people in policymaking). This perspective resolves previous theoretical anomalies of union behavior; provides many new avenues for research; and highlights distinct considerations for the practice of teacher organizing.