Researchers, policymakers, and the public are increasingly interested in judging colleges and universities on measures beyond selectivity and prestige. When Opportunity Insights compiled the first-ever dataset to highlight colleges that are the best at promoting economic mobility among students, these groups embraced the new information with enthusiasm. This report discusses the following key points: (1) Policymakers and the media are enthusiastic about ranking colleges based on students' economic mobility, but some healthy skepticism is warranted; (2) Ranking colleges and universities based on students' economic mobility can unfairly advantage institutions in places with extreme income inequality; (3) In one highly regarded mobility ranking, three states--New York, California, and Texas--accounted for 75 percent of all high-mobility colleges, even though these states are home to just 23 percent of higher education institutions; and (4) Data limitations from this popular ranking method effectively exclude one in five colleges from its results, even many prestigious state universities.