Success Boston, a city-wide initiative to boost college persistence and ultimately improve college completion rates for Boston's high school graduates, has one-on-one transition coaching as a core strategy. Transition coaching offers students sustained, proactive, and responsive support in their first two years of college. Specifically, coaches help students navigate the academic, financial, career, and personal aspects of college through one-on-one meetings, phone calls, emails, and text messages. In addition, coaches refer students to resources and services on their campuses. By providing these supports, Success Boston coaches aim to help students succeed in college and ultimately complete their degrees and certificates. This report examines the impacts of Success Boston Coaching (SBC) on college completion, college persistence, and academic achievement for four cohorts of students: the Boston high school graduates from the Classes of 2013 and 2014 (cohorts before the scale-up) and 2015 and 2016 (cohorts after the scale-up). Using a quasi-experimental design, the evaluation compares persistence and completion rates for the students who participated in SBC ("treatment" group) versus those of a group of similar students ("comparison" group) who did not participate in SBC. As such, the report provides evidence that observed differences in outcomes between the two groups are due to SBC. [Written with Beth Gamse.]