John Dewey’s conception of “public interest” is complex and provocative. For Dewey, public interest differs from interests in the plural, as in “I have my interests and you have yours.” Public interest differs from any a priori interest or concern. It is never settled or fixed in form. Rather, Dewey argues that public interest is always emergent and dynamic. Its appearance is often highly unpredictable. Public interest emerges when an action in a particular domain of life has consequences that spill over into other domains of life and have a noticeable impact on them. In such circumstances, persons with widely different interests may find themselves responding, together, to the new action in shared ways. I illustrate Dewey’s conception by touching on the NCLB legislation (2002) with its focus on quantitative measurement of learning. As has been widely reported, NCLS has triggered critical responses from many groups in the nation: teachers, administrators, educational researchers, parents, and more. These groups sometimes do not see eye to eye on educational matters. Their “interests” sometimes differ, and markedly so. However, through their visible, critical response to the NCLB law, they have generated what Dewey would call a public in which they are enacting public interest—precisely in their emergent, collective response.