This paper explores what happens to similar groups of children educated in different school districts. In this case, the "twins" in the study are groups of students who live in the same state in similar geographies and who share certain demographic characteristics. For this report, "twin districts" have very similar sizes and they have the following in common: (1) The proportion of students who are from low-income families; (2) The proportion of students who have limited English proficiency or are English language learners; and (3) The proportion of students who receive instruction through individualized educational programs. The study's twin districts, however, differ in terms of per-pupil spending and revenues. The goal of this paper was to study twin districts and use the data culled to provide recommendations for how districts can best leverage their school funding investments--in other words, achieve a bigger bang for their educational buck. Using data available from the U.S. Department of Education, the authors compiled a dataset with over 7,000 K-12 districts from over 15,000 local education agencies across the county. All data on spending and achievement was from the 2009-10 school year. In this analysis, they identified 424 pairs of districts to analyze from this larger dataset. Given that tests and proficiency definitions differ across states, only twin districts within the same state are identified and compared. Additionally, the authors also completed interviews with 20 district superintendents from across the United States to discuss what control they have over their districts' spending and what spending constraints they face from outside governing bodies--the state, the federal government, and school boards. Based on their in-depth look at twin districts and their subsequent analysis of the data, the authors offer the following findings: (1) When it comes to education, spending does not always equal results; (2) There are significant funding inequities between demographically similar districts; and (3) Districts have limited control over their own expenditures. A table showing descriptive statistics for 424 sets of twins from the 2009-10 school year is appended. [For the accompanying report, "Return on Educational Investment: 2014. A District-by-District Evaluation of U.S. Educational Productivity" (2014), see ED561093.]