Prior research suggests that some social media practices can play a role in shaping students' adjustment to college; however, the specific mechanisms by which social media can support the identity work associated with successful transitions to college are not well understood. This paper investigates how social media experiences and interactions can support college-focused identity construction for low-income, first-generation college students. Drawing on in-depth, semi-structured interviews with 31 emergent adults from disadvantaged backgrounds in the United States, we identify social media affordances that support the process of identity work during a critical transition period. Findings indicate that social media platforms support provisional identity work, but disadvantaged college students lack access to mentor-like figures that could be accessible through social media. We also find barriers to sharing information online that may extend to other life transitions in multiple life contexts and review the design implications of our findings.