The study attempted to trace the relationship between facility with cardinal-ordinal aspects of number; attention to dimensions of number, length, and density; and the presence and absence of number conservation. On the basis of performances on the standard test for number conservation, 25 nonconserving kindergarteners, 34 conserving kindergarteners, and 21 conserving third graders were chosen and cardinal-ordinal ability was assessed by a standardized version of Piaget's classic task. Attention was assessed by presenting three rows of poker chips so two could be chosen the same on the basis of number, length, or density. Results suggest that attentional and cardinal-ordinal abilities are related to the development of number conservation. (Author/DT)