A college degree typically helps graduates earn more when they enter the labor force and is a key driver of economic mobility. However, many students who enroll in college do not finish, reflecting numerous academic, financial, and social emotional barriers students may face to succeeding in college and completing a degree, from being underprepared for college coursework to struggling to afford tuition or other expenses like books and housing. The COVID-19 pandemic brought additional challenges and amplified existing ones (U.S. Department of Education 2021; Hotez et al. 2022). Funded by The Boston Foundation, Success Boston brings together Boston Public Schools (BPS), local colleges and universities, the City of Boston, and various nonprofit organizations. In 2022, the initiative recommitted to improving BPS graduates' postsecondary completion rates, with a target rate of 70 percent across all groups of students (The Boston Foundation 2022). A core strategy of Success Boston, transition coaching offers support to students in addressing challenges they face in college. The Success Boston Coaching (SBC) model matches recent graduates of BPS with a coach, who meets with them regularly during their first two years of college and supports them as they navigate academic, financial, and social barriers. Our quasi-experimental study looks at SBC's effects on students' four-, five-, and six-year postsecondary completion rates, across more than 9,000 students across 50 colleges who initially enrolled in college in 2015, 2016, or 2017. To do this, we conducted propensity score matching to construct a comparison group with similar demographic and baseline academic achievement to SBC students, and who enrolled in the same college in the same year. To measure SBC's effects, for each outcome, we estimate a linear regression model that includes indicators for matching blocks and matching characteristics, among the matched comparison and SBC students. We find that students who received SBC graduated in four years at rates that are 21 percent higher than those of noncoached students and in five years at rates that are 15 percent higher. These effects are meaningful because completing college in four years or five years, rather than in six or more years, can help students avoid the costs of additional years of college and allow them to enter the labor market sooner. At six years after entering college, differences in graduation rates between coached and noncoached students were no longer statistically significant, suggesting that some noncoached students had caught up to the coached students at this point. Findings suggest that the coaching program could be an important component in helping move citywide postsecondary completion toward its of 70 percent target. That said, only about 49 percent of coached students, and a similar proportion of all BPS students, complete college in six years, well short of the 70 percent target. Students will continue to need support, perhaps through extending coaching beyond students' first two years in college, for the city to achieve the initiative's goal. To focus its efforts on students who could most benefit from the support, SBC serves primarily students from groups traditionally underrepresented in postsecondary education, such as members of racial/ethnic minority groups and students from economically disadvantaged backgrounds.