The purpose of this study was to investigate teacher leaders' perceptions of the use of humor in the high school classroom. For the purposes of this qualitative research the case study method was used. The question of what makes teachers successful with their use of humor in the classroom has been divided into four categories: climate, communication, engagement, and relationships. Nine high school classroom teachers from various curriculum areas comprised the sample. This research was completed using a case study methodology allowing for observations of teachers and personal interviews. Two observations of each classroom were completed during a 10-day period during spring 2012. Following the classroom observations, these teacher leaders participated in interviews about their perceptions of the use humor in the class and then they discussed their conceptions in a focus group format. Coupled with the information garnered during the classroom observations, the teachers' responses during the interviews and focus groups provided information about their attitudes toward the use of humor in the classroom. The use of teacher leaders' humor in the classroom has not previously been studied at the high school level in any detail. Based on the information gathered, as well as teacher comments, conversations, and discussions, it is clear that these teacher leaders all believe that humor makes instruction more effective. Using humor supports the classroom climate and the communication between students and teachers and their relationships and it also, encourages engagement. All of these topics, which are key to successful instruction, are covered in this study. A significant finding from this study is that teacher leaders support the use of humor in their effective instruction. [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.]