The concept of a round Earth is not a simple one for children to acquire. Their everyday experience reinforces their deelply held notion that the Earth is flat. Told by adults that the Earth is round, they often react by constructing a mental model of the Earth as a pancake, or a terrarium -like structure with people living on the flat dirt layer inside, or even a dual model with a spherical Earth and a flat Earth coexisting simultaneously. In effect, children attempt to accomoodate the new knowledge within the framework of their existing conceptual models. Unfortunately, holding tight to the features of the prior models inhibits fundamental conceptual change.