First-year seminars (FYS) comprise one of 11 researched interventions in postsecondary education known as High-Impact Practices, but few rigorous studies report significantly high impacts. This study examined a FYS employing propensity score matching to link cases and controls in a quasi-experimental design. One semester later cumulative grade point average (GPA), cumulative hours attempted, and 1-year later indicators (hours earned, hours attempted, and term GPA) were statistically different between the two groups. Three freshman survey items were also statistically significant and differences were observed within the same semester of the program. Quantitative differences did not appear immediately but appeared one term and 1 year later. Mean differences did not appear to diminish between groups over time. This analysis helps to fill a void in the paucity of studies clarifying the relationship between FYS participation and outcomes using comparison groups.