With adolescent mental health problems on the rise, secondary school teachers are in a prime position to support students. This study sought to fill a scholarly research gap and inform future mental health literacy (MHL) training needs for teachers and to identify implications for their professional practice. Specifically, this study sought to address the limited research available on the newly deemed "at-risk" population of students in high achieving schools (HASs) enrolled in accelerated courses taught by Advanced Placement (AP) teachers. The purpose of this basic interpretive qualitative study was to investigate the perceptions of high school AP teachers in HASs regarding MHL by understanding how they perceive and develop their MHL knowledge base, the effectiveness of training they have received, and the relationship between their MHL knowledge and professional practice. Results of the study from semi-structured one-on-one interviews with five high school Advanced Placement (AP) teachers within a HAS indicated that the MHL knowledge base of these teachers was inadequate for supporting students with mental health problems. Further, results indicated that the MHL training that they have received was insufficient, leading them to rely on experience beyond in-school training to develop knowledge. Implications of the study suggest a need for targeted, comprehensive pre-service and school-level MHL training and curriculum for high school AP teachers to be developed, integrated across courses, and monitored. [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.]