This study takes advantage of the unexpected announcement of the Kalamazoo Promise to study its effects on student achievement and behavior in high school. The Kalamazoo Promise provides college scholarships to graduates of Kalamazoo Public Schools (KPS), a midsized urban school district in Michigan that is racially and economically diverse. Anonymous donors promise to pay up to 100 percent of college tuition for any KPS graduate who attends a public college or university in Michigan. Scholarships start at 65 percent of college tuition for students who enrolled in KPS in 9th grade and stay until graduation, and increase to 100 percent for students who have attended since kindergarten. Specifically, this study examines how the achievement and behavior of individual students eligible for a tuition subsidy changed after the program was launched. The data come from Kalamazoo Public School administrative records. The authors examine data on 9th- through 12th-grade students from the school years 2003-04 to 2007-08. This period includes two pre-Promise school years, the year the Promise scholarship was announced, and two post-Promise school years. The information on each student includes demographic characteristics, credits completed, grade-point averages, and disciplinary actions, including days of suspension and detention. The authors find clear evidence that the Promise reduced student behavior problems. Results on academic performance for all students are unfortunately not precise enough to draw strong conclusions.