["Journal of Research on Adolescence, Volume 36, Issue 2, June 2026. ", "\nAbstract\nAlthough adolescence is theorized to be a critical period for identity development, little is known about how gender identity, specifically gender centrality and private regard, develops among adolescents. The current study assessed trajectories of gender centrality and private regard across five waves of data from Grade 9 through Grade 10 among cisgender adolescents from the United States (Mage = 14.1 years; N = 374; SD = 0.41, 139 boys and 235 girls). Additionally, the study explored how gender centrality, private regard, and their development were related to later psychological and social well‐being. Initial levels of gender centrality and private regard did not differ by gender. However, boys showed declines in their levels of gender centrality and private regard, whereas girls remained stable. For girls, higher initial levels of gender centrality and private regard were associated with greater psychological and social well‐being. Additionally, increases in positive regard were associated with increased psychological well‐being one year later. Boys' gender identity was unrelated to their well‐being. Findings underscore the importance of assessing gender identity as a developmental construct among middle adolescents and the implications that gender identity can have on the well‐being of adolescents.\n"]