This study compared the effects of a formal, an open-framework, and a control preschool program on children's intellectual development. The formal program, based on Ausubel's and Piaget's theories, had a daily schedule of short prescriptive teaching sessions followed by related learning activities. The informal program, based on Piaget's theory, relied on teachers to stimulate the children to assume self-initiated activity rather than to provide direct instruction. The control program was a traditional play-oriented approach not based on any particular theory of intellectual development. Pre- and post-testing were done with the Peabody Picture Vocabulary Test, the Raven Coloured Progressive Matrices Test, and a series of logical concept tasks assessing relations, classification, and conservation. At midyear, a sample of children from each experimental group was assessed with a battery of classification and conservation tasks which, unlike the pre- and post-tests, included content selected by teachers from the learning materials in their programs. A delayed post-test was administered to the Ausubelian and control groups but not to the Piagetian group due to its excessive subject attrition. Based on the overall results, it was concluded that both experimental models were superior to conventional preschool programs in enhancing the growth of logical concept attainment and that the Ausubelian model was more effective in facilitating development of such concepts in the short run. (Author/JMB)