Grit, defined as perseverance and passion for long-term goals, has garnered attention in educational research for its potential to predict academic achievement and well-being. Despite this, its psychometric properties and applicability across diverse populations remain underexplored. This study aims to validate the Grit-O scale and explore its relations with various psychosocial and academic outcomes among underrepresented undergraduate STEM scholars. Analyses utilized a mixed-methods approach, including confirmatory and exploratory factor analyses, bivariate correlations, and moderated multiple regression analyses. Results indicate that the Grit-O scale did not demonstrate adequate fit in its original form. However, an amended 11-item scale comprising two correlated factors (perseverance and consistency) showed improved fit and was retained for further analysis. Exploratory analyses revealed consistent factor structures across binary gender groups, suggesting scale robustness across gender identities. Neither perseverance nor consistency significantly predicted entry into a STEM graduate program. The intricate relationship between grit and various academic and psychosocial outcomes offers valuable insights into the influence of perseverance and consistency. Correlations and moderated multiple regression analyses highlight nuanced associations between grit dimensions and academic and mental health outcomes. This study sheds light on Grit-O's psychometric properties, but its utility for measuring academic achievement remains inconclusive. The mixed findings underscore the need for continued psychometric scrutiny and a nuanced understanding of academic achievement dynamics, particularly for underrepresented groups. Future grit research should prioritize rigorous validation of the measure to ensure that the model appropriately fits the population and can be reliably used to draw meaningful conclusions. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]