To study the developmental interrelationships among various aspects of logico-mathematical knowledge, 80 one- to 4-year-olds were individually asked to build "something tall" with 20 blocks. Percentages of new and significant behaviors increased with age and were analyzed in terms of the development of logico-mathematical relationships. It was found, for example, that the new spatial relationships children made as they grew older also changed the classificatory, seriational, numerical, and temporal relationships they made. The educational implication drawn is that it is better to define objectives for preschool mathematics education in terms of the development of logico-mathematical knowledge rather than the learning of specific aspects of elementary school mathematics. More broadly, an argument is made in favor of encouraging preschool children to think and make many mental relationships rather than to teach them specific subject matter. (Contains 1 table and 9 figures.)