We examined longitudinal changes in new college students' perceptions of belonging and task mastery socialization effectiveness and their relationships to re-enrollment intentions and subsequent GPAs as a function of race/ethnicity and first-generation status. Incoming students completed socialization effectiveness measures before orientation (N = 2,320), after orientation (N = 1,867), and during a first-semester student success course (N = 324). The results from the sample of 302 students who completed the course indicated that students, especially students of color, experienced greater task mastery versus belonging as the semester progressed. Students who perceived greater belonging (but not task mastery) had stronger intentions to re-enroll; this was especially true among Latinx (vs. non-Latinx) students of color, White (vs. students of color), first-generation students, and students of color (vs. White) continuing-generation students. In contrast, students who perceived greater task mastery (but not belonging) had higher GPAs and this was more true of Latinx (vs. non-Latinx) students of color. These findings support the use of a brief measure to assess socialization effectiveness and suggest that early belonging and task mastery interventions might be effective for improving retention and performance, respectively. They also suggest that more targeted interventions may be needed to improve underrepresented group members' perceptions of belonging.