This study examines the costs of a large scale initiative to create new, small high schools in New York City.   A recently published evaluation of this initiative which exploits randomly assigned high school admissions has found that attending a new, small high school increases graduation rates by 9.5 percentage points relative to attending other New York City high schools.   The push for small high schools has been prominent in the discussion of high school reform for over a decade, and combined with the recent evaluation of the benefits of New York City’s small high schools , the present study helps to inform assessments of the small school movement.  In addition, the analysis contributes to the development of methods for evaluating the costs of educational interventions by carefully identifying the policy questions that a cost analysis might address, illustrating how school level expenditure data can be used in combination with a random assignment research design to address questions about costs, and by paying careful attention what different types of analysis imply for different policy questions.  The study findings indicate that the value of resources per pupil used is greater in a set of New York City’s new small high schools than in large New York City high schools.  Nonetheless, when using the experimental framework established by the recently conducted evaluation of the effect of attending one of these small high school on graduation rates, the control group students also tended to enroll in schools with above average per pupil resource use.  Thus, we find the positive effects on graduation rates were achieved without devoting any more resources to students in these new, small schools than were devoted to control group counterparts.  We carefully consider the implications of these results, and conclude that they provide strong rationale for considering the small high schools in New York City a success that ought to be continued.  As we discuss, however, implications for the expansion of the small schools initiative either in New York City or to other urban areas are less certain.