This study explores the impact of Pedagogical Content Knowledge (PCK) on assessment practices and their subsequent influence on student learning outcomes. Through case studies of three educators—Ms. Sarah Thompson at Lincoln Middle School, Mr. David Martinez at Crestwood High School, and Ms. Emily Chen at Brookfield Elementary School—the research examines how deep subject matter expertise and pedagogical strategies shape both formative and summative assessments. The findings reveal that effective integration of PCK into assessment practices enhances student performance, engagement, and feedback quality. Despite these insights, the study acknowledges limitations such as context-specific findings and qualitative data reliance, suggesting the need for further research across diverse settings and methodologies. The study highlights the importance of PCK in creating equitable and effective assessments and provides implications for educational practice, professional development, and policy.