The study aimed to examine and interpret the experiences of an experienced science teacher in Real Engagement in Active Problem Solving Model (REAPS) implementation conducted within the Electricity Unit through a validated pedagogical content knowledge (PCK) framework. To this end, the study examined the efforts of an experienced middle school science teacher, in helping her seventh graders in a rural public school improve conceptual understandings of electricity. She was an information-rich teacher and agreed voluntarily participation in the study. The study was based on a basic qualitative study design. REAPS interview questions and guiding interview questions with prompts were employed as the data collection tools. The data were analysed via in-depth analysis of explicit PCK, enumerative approach, and constant comparisons. The results revealed various characteristics of the usage of REAPS Model, the interactions between the PCK components, and emerged critical incidents in teaching practice. Regarding the usage of REAPS Model, the science teaching experience of the participant teacher was expanded with the themes of engagement, real-life experiences, socialization in diverse cultural contexts, teaching in varied physical conditions through argumentation and retention. As an experienced teacher, the interactions between knowledge of learners and knowledge of instructional strategies were central in the teaching performance of the participant teacher. Self-efficacy was specifically found conducive for triggering these interactions together with knowledge of curriculum. However, her science teaching orientation impeded the interactions between most of the PCK components. Finally, critical incidents were found beneficial to the investigations looking for the interactions between three or more PCK components, in particular.