This case study examined the concerns of an experienced elementary physical education teacher implementing a curricular innovation. Aware of current physical education practice, the teacher experimented with a tactical approach to teaching games, which was a departure from his previous 20 years of experience teaching games from a technical perspective. The theoretical perspective that framed this study was developmental stage theory, and in particular, Fuller’s teacher concerns model. According to Fuller, teachers develop along a progression of concerns. The first has been labeled the “Phase of Concerns about Self” (Phase I). Once they are given an opportunity to teach, they tend to enter into the second “Phase of Concerns about Self as Teacher” (Phase II). Their concerns relate to their ability to teach proper content, as well as manage a class. Once they have matured in relation to these concerns teachers usually enter into the final “Phase of Concerns about Students” (Phase III), whereby their major concern is pupil learning. Although Fuller originally developed the concerns model studying pre-service teachers, she also studied more experienced teachers. What concerns would this experienced teacher have initially as he taught utilizing a different approach, and would his concerns change over time? Seventy-four fourth grade students were also given a pre- and post-instruction questionnaire to determine if their declarative knowledge pertaining to game play was influenced by the innovation. Phenomenological data were collected on the teacher through three semi-structured interviews, as well as a journal updated daily by the teacher. Interviews were transcribed within a week of completion. Lessons were videotaped and analyzed to ensure fidelity to the teaching approach. All data pertaining to the journal, interviews and questionnaire were analyzed inductively, utilizing the constant comparison technique and were checked by a peer reviewer. Data revealed that the teacher initially experienced considerable anxiety when implementing this new approach. His concerns included the acceptability of a tactical approach to his students, his ability to prepare and organize tactical lessons, and the appropriateness of his content delivery. Initially, he was in Fuller’s Stage II, with major concerns for himself as a teacher. One-third of the way through this study (15 classes), his concerns shifted to student performance (Stage III), while his teaching focus shifted from skill development to game play performance. After exposure to the tactical approach, the students expressed their declarative knowledge related to game play more completely and clearly. Keyword(s): elementary education, professional development