Approximately 10% of U.S. children are diagnosed with ADHD, and the majority of them retain clinical levels of ADHD symptoms as an adult. Among them, comorbidities are often observed, which can negatively impact a broad range of their everyday life including social, emotional, behavioral, and academic/work functioning. A first-line treatment option of medication is available but it may cause inadequate responses. It is meaningful to diversify psychosocial interventions for the heterogeneous ADHD population. Currently, CBT and mindfulness-based interventions are evidence-based interventions. However, most ADHD intervention studies do not address unique challenges of college students with ADHD. They play a role as an emerging adult as well as a student in formal educational settings. During the transition, college students with ADHD may experience more difficulties navigating their life without the same structures from their parents and schools. This study aims to answer this question: Can adding mindfulness components into CBT-only coaching substantially improve the clinical effectiveness in ADHD symptoms, psychological health, and academic achievement outcomes among college students diagnosed with ADHD? In a non-concurrent multiple baseline single case subject design, four participants completed 12 coaching sessions. The results are conflicting. First, adding mindfulness to CBT-only coaching did not significantly improve ADHD symptoms or academic achievement outcomes. However, in psychological health outcomes, it showed more effectiveness than CBT-only coaching but the levels of significance range from weak to strong. Based on the results and limitations, implications for both practitioners and future researchers follow. In the discussion section, clinical change mechanisms and intervention planning depending on students' characteristics are highlighted. [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.]