With an impetus towards science reform in the United States, citizen science is emerging as a platform with the potential to transform student learning and engagement. While current citizen science studies predominantly focus on student outcomes, there is little empirical evidence that captures the voices of teachers who voluntarily implement citizen science to meet the needs of their students. The purpose of this interpretive phenomenological analysis (IPA) study was to understand the lived experiences of six K-12 science teachers in the United States who implemented citizen science within their schools. The ecological model of teacher agency, teacher beliefs, and sensemaking were employed as a conceptual framework, and served as a means of examining teacher perceptions of implementing citizen science in a voluntary capacity. Data was collected using semi-structured interviews and yielded four superordinate themes: philosophies on citizen science, the value of resources and support, citizen science impacts, and challenges. An additional finding--the teacher's role as intermediary--was discovered through in-depth analysis. The findings revealed teachers' positive beliefs about students and citizen science outweighed the cost of any challenges. Participants respected and recognized the importance of science content; however, citizen science was a vehicle for students' deeper and broader knowledge-making, developing connections, and forming agency. Additional research is needed to explore how teaching through the lens of culturally relevant pedagogy may enhance student experiences with citizen science that leads to increased learning and engagement. [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.]