Since the introduction of international achievement assessments, Korea has received a great deal of global attention because of its strong academic performance achieved at primary and secondary education levels. However, Korea has not fully benefited from these achievements in education for several reasons as discussed in this paper. The Korean education system is now faced with challenges that have emerged from these achievements. The purpose of this paper is thus to discuss the curriculum reforms in Korea, which were undertaken to achieve sustainable success and meet the challenges of the twenty-first century learning ecology. This paper highlights that beneath its high academic performance, the Korean educational system faces problems related to students' low interest levels in learning, a declining index of students' happiness, and increasingly deskilled teachers because of the prescribed national curriculum. This paper describes the current shift taking place in the Korean educational system as it move from knowledge delivery to competency development, from academic excellence to student happiness, and from centralized and detailed prescriptions to more autonomous decision making by teachers in order to overcome these problems and respond actively to twenty-first century learning ecology. In addition, this paper suggests that changes must be followed in terms of school practice, teachers' professional development, and sociocultural structures as means of achieving these reforms.