This paper presents case studies of two teachers at Crescent Girl's School (an all-girls high school in Singapore) who implemented strategies learned through a teacher professional development program called 21st Century Learning Design (21CLD). Policymakers often state requirements for teachers to focus on 21st century (21C) competencies without providing them with the necessary pedagogical support and training needed to support students in developing these competencies. 21CLD fills this gap by offering concrete rubrics, definitions and examples in six "dimensions" that each relate to a 21C competency--collaboration, real-world problem-solving and innovation, knowledge construction, use of information and communication technologies (ICT) for learning, skilled communication, and self-regulation--to support teachers as they build these ideas into their lessons. In this paper we provide evidence of the influence of 21CLD on two teachers' instructional practice. The first case study describes a science teacher's experience using the 21CLD frame to revise a lesson to focus more deeply on developing students' collaboration skills. The second case study highlights a mathematics teacher's experience with developing and implementing a new mathematics lesson to develop students' real world problem-solving skills. These case studies highlight the valuable role that 21CLD has played in enhancing teachers' instructional practice by providing a common language and understanding of 21C competencies, and supporting a vibrant and dynamic professional learning community. [For full proceedings, see ED557168.]