Although high school graduation rates are improving, a large number of students are still not successful. Research has documented that 9th grade is a pivotal year in determining whether a student will graduate or drop out. The purpose of this randomized controlled trial was to assess the effects of a Tier 1 intervention model (Freshmen Success) for 9th graders to increase school engagement, attendance, credits earned, and grade point average (GPA). This study included 1,588 students in 9th grade across four comprehensive high schools. Treatment schools implemented the Freshmen Success components: a 9th grade Leadership Team, a curriculum, and support from Peer Navigators. Control schools continued business as usual. Results showed statistically significant and educationally meaningful effects on student motivation, engagement and attendance, and a moderate-to-large effect for credits earned; however, there was no significant effect found for GPA. Impact and Implications Statement: This study demonstrates that the FS model, when implemented with fidelity, increased 9th grade student engagement, attendance, and credits earned. However, the intervention was not associated with significant improvements in GPA [The paper will be published in "School Psychology."]