This study examines academic trends in learning and assessment theories based on the OPPA (One Page Portfolio Assessment), which was developed in 2002. The study also clarifies the theoretical framework, teaching practices, application, and effectiveness of the OPPA. The OPPA was developed to solve three teaching and learning challenges: (1) how to cultivate abilities and competencies in learners, (2) how to validate that this is achieved, and (3) how to help teachers in improving their teaching. First, to gain an overview of the OPPA, this study examines its basic structure and theoretical framework using the following five points: (a) an academic achievement model that focuses on the formation and acquisition of achievement; (b) a portfolio assessment that focuses on learning processes and change; (c) diagnostic, formative, and summative evaluations on one page; (d) cultivation of learners' competencies by internalization, reflection, and externalization of thought and cognitive processes; and (e) a retrospective self-evaluation of the entire learning. This study then examines the creation of teaching plans and OPP sheets, the application of teaching and learning practices with these sheets, and methods to improve lessons using the sheets. On the basis of the responses of learners who used the OPPA method, its effectiveness is outlined in nine points, such as its capability to transform learning and impart to learners the significance and necessity of learning. Finally, this paper touches on issues not covered by the OPPA, such as teaching methods to increase the competencies of all learners. (Contains 5 notes and 5 figures.)