This article explores the theory of action underlying New York University's (NYU's) Partnership Schools Program--explaining in the process what a theory of action is, and how it can be constructed for other innovations in other contexts. NYU's Partnership Program involves 23 schools, K-12, spanning several of New York City's most economically disadvantaged neighborhoods. It operates on the basis of what the authors call "mutual self-interest" and exploits what they call "complementarity." The authors illuminate the program's original as well as its evolving intentions, and the environmental conditions necessary to enact them and to sustain the program over a decade. They also describe the program's core design elements, with a view to how these may be replicated elsewhere. Finally, they look closely at the Partnership's theory of action "in action", employing action research data to portray a meeting where professors and teachers discuss the teacher education residency experiment they have collaboratively launched.