This paper identifies fundamental issues regarding the curricular link between kindergarten and elementary school based on the PYP implementation experiences at Yamanashi Gakuin Kindergarten and Elementary School, which became the first nine-year PYP authorized article-one school in Japan. The underlying issues identified are: (a) a lack of common knowledge shared by the kindergarten and elementary school; (b) a focus on subject learning in elementary school; and (c) the nature of qualitative assessment practices in kindergarten and elementary school. To address the issue in (a), the study suggests building a shared view of learning, curriculum, and educational assessment based on a common “inquiry-based” format in order to create a stronger transition between the kindergarten and elementary school. Furthermore, to address issue (b), a project-based approach with an emphasis on reflection is proposed to link “comprehensive learning time” and subject-specific learning. Finally, to address issue (c), “WEWE”should be discussed to facilitate qualitative assessment practices of “inquiry-based activities” by teachers.