 Good teaching, then, is built around the operational abilities of the students such that they can excel in their operational stage and build on preexisting structures and abilities and thereby "build" learning.Evidence of the effectiveness of a contemporary curricular design building on Piaget's theories of developmental progression and the support of maturing mental structures can be seen in Griffin and Case's "Number Worlds" curriculum.The curriculum works toward building a "central conceptual structure" of number sense in young children by building on five instructional processes, including aligning curriculum to the developmental sequencing of acquisition of specific skills.