Problem-based learning has long been recognized as an innovative and effective instructional strategy for enhancing problem-solving and critical skills, which are essential for 21st-century employability. Despite its recognized benefits, PBL adoption in K-12 education remains limited due to significant implementation challenges. This integrative literature review investigates PBL instructional strategies and teachers' experiences, focusing on their challenges and the types of problems used in K12 classrooms, while analyzing empirical studies from 2004 to 2024. The study findings reveal teachers' challenges in terms of problem design and development, scaffolding, technology integration, assessment, and promoting student collaboration, with time availability being a recurring concern. Again, teachers' implementation strategies are flexible but could, however, be summarized into (1) preparing learners for PBL, (2) an iterative cycle of activities, and (3) presentation and evaluation. The findings also revealed that design problems dominate the type of problems that are incorporated into K-12 PBL implementation studies. Beyond setting the foundation for future research in the area, this integrative review offers a deeper understanding related to PBL's application in K-12 settings, providing valuable insight for educational stakeholders. / Doctor of Philosophy / Problem-based learning (PBL) is a student-centered teaching method that supports the development of relevant problem-solving and critical-thinking skills which are critical for career success and employability in the 21st century. Although many studies have emphasized its effectiveness, it is not widely used in K-12 education. This limitation is attributed to different implementation challenges. This integrative literature review investigates PBL instructional strategies and teachers' experiences, focusing on their challenges and the types of problems used in K-12 classrooms, while analyzing empirical studies from 2004 to 2024. The study findings reveal teachers' challenges in terms of problem design and development, scaffolding, technology integration, assessment, and promoting student collaboration, with time availability being a recurring concern. Again, teachers' implementation strategies are flexible but could, however, be summarized into (1) preparing learners for PBL, (2) an iterative cycle of activities, and (3) presentation and evaluation. The findings also reveal that design problems dominate the type of problems that are incorporated into K-12 PBL implementation studies. Beyond setting the foundation for future research in this area, this integrative review offers a deeper understanding related to PBL's application in K-12 settings, providing valuable insight for educational stakeholders.