Attention Deficit/Hyperactivity Disorder (ADHD) is one of the most prevalent childhood disorders in the United States. Although many children with an ADHD diagnosis are prescribed medication to control symptoms, behavioral concerns are still regularly noted in the classroom, home, and other settings. Therefore, school psychologists are often called upon to assist teachers and families with developing intervention procedures. The purpose of this research was to investigate the relationship between mindfulness training, the cognitive processes of attention regulation, and behavior of children who have been diagnosed with ADHD. This study utilized a multiple baseline across participant's design where each student was tracked over time following a baseline (pre-intervention) condition. Four 8-year-old male participants with a primary diagnosis of ADHD and a significant number of off-task classroom behaviors were included in this study. Teacher and parent ratings of the Behavior Assessment System for Children, Second Edition (BASC-2) and Behavior Rating Inventory of Executive Function (BRIEF) were completed pre- and posttest for each participant. The Reliable Change Index (RCI) was calculated to determine if the pre- to posttest change scores on the BASC-2 and BRIEF exceeded what could be accounted for by measurement error alone. Results of the analyses revealed that mindfulness training was effective in increasing the number of on-task behaviors for participants. Parent and teacher ratings on the BRIEF suggest that mindfulness training impacted ratings on the Inhibit, Initiate, and Monitor scales. Parent and teacher ratings on the BASC-2 were analyzed and scores from the Attention Problems scale did not demonstrate significant change across raters and across participants. Significant change occurred on the Hyperactivity scale. Findings are discussed in relationship to the literature on mindfulness training for students with a diagnosis of ADHD. Implications for future research and practice are also suggested. [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/en-US/products/dissertations/individuals.shtml.]