This study critiqued the nature of understanding in the context of the International Baccalaureate Primary Years Programme (IBPYP) and evaluated the arrangement of understanding goals in written curricula and in the context of the IBPYP. The methodology was a literature review: a critique and analysis of the work of leading authors in the field of teaching for understanding and concept driven curricula. The key findings of the work were that understanding is poorly defined both in curricula generally and in the IBPYP. Understanding arises in learners as mental models and as actions resulting from these thought processes. However its most useful, measurable manifestation is flexible performance ability. Understanding goals - known as central ideas in the IBPYP - were found to be beneficial in providing connectivity and scope to inquiries but to be lacking in provision for disciplinary depth. The work recommended that the IBPYP should address its definition of understanding by advocating and defining a flexible performance ability stance to understanding. The study also advocated the addition of nested understanding goals in the PYP unit planner.