The primary aim of the first study in this dissertation was to adapt two existing measures, Identity Management Strategy Scale and Outness Inventory, assessing multidimensional disclosure and concealment construct to be developmentally appropriate for sexual diverse youth in the school context. Both adapted measures were sent to experts in the field for face validity evaluation. Psychometric evaluations were conducted with confirmatory factor analysis, measurement invariance test, reliability test, and convergent and divergent validity tests. We recruited 420 sexual diverse youth aged between 14-24 (M = 18.28, sd = 2.21) and recruited from the Qualtrics Panel Service. Results from psychometric evaluations of both adapted measures demonstrated good factor structures and validity. The adapted Outness Inventory was also found to be reliable, but the adapted Identity Management Strategy Scale only showed good reliability in the decategorizing and integrating subscales but not in the assimilating subscale. Measurement invariance tests showed that the assimilating subscale from the adapted Identity Management Strategy Scale needs to be used with caution about mean differences in the report scores between monosexual (i.e., gay and lesbian) and plurisexual youth (i.e., bisexual, pansexual, queer, etc.) The primary aim of the second study in this dissertation was to expand on the disclosure process model from multidimensiaonal perspectives using the adapted measures from the second study. Using the same data introduced in the first study, the second study examined whether school policy contributes to various aspects of disclosure and concealment (i.e., assimilating and decategorizing concealment behaviors, integrating disclosure behavior, outness level, and openness level) through positive and negative school climate, and whether such various aspects of disclosure and concealment contribute to sexual diverse youth's psychosocial outcomes (i.e., depressive symptoms and life satisfaction) through perceived school support and experiencing sexual orientation-based victimization. Results from the predictors of disclosure and concealment model showed that inclusive school policy was negatively associated with decategorizing concealment behavior, and positively associated with integrating disclosure behavior and openness level via higher levels of perceived positive school climate. Inclusive school policy is also negatively associated with decategorizing concealment behavior via lower levels of perceived negative school climate. In addition, positive school climate was positively associated with outness level. Results from the outcomes associated with the disclosure and concealment model showed that decategorizing concealment behavior was negatively associated with school support and positively associated with depressive symptoms. Integrating disclosure behavior was positively associated with school support. School support was positively associated with life satisfaction. Sexual orientation-based victimization was positively associated with life satisfaction and was negatively associated with depressive symptoms. Overall, this dissertation contributes to the literature by providing two reliable and valid measures allowing researchers to assess multidimensional construct of disclosure and concealment. This dissertation also highlights that each aspect of disclosure and concealment (i.e., behavior, outness, openness) has unique contributions to sexual diverse youth's experience in the school context. Furthermore, this dissertation recommends future studies integrating contextual and interpersonal factors when understanding sexual diverse youth's disclosure and concealment experiences in school. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]