ations substage and lasts from about the seventh year to the eleventh year. To Piaget, an operation is defined as perceptual action or movement which can return to its starting point and can be integrated with other actions also possessing the feature of reversibility (Athey, 1970, p. 231). A concrete operation is therefore the coordination and internalization of perceptual actions that have been made on a concrete object. Piaget also found that the ability to use formal operations sometimes develops without instruction, but it is not adequate to encompass the results, thinking, or attitudes of modern science. There develops a kind of "common sense" that does not enable them to recognize the type of relationship one has to recognize when one makes a scientific study. In science instruction, a qualitative change in learning can occur if one develops in the student's thinking about natural phenomena, a hierarchical structure of concepts that later becomes increasingly sophisticated. Each topic in the science program should represent an application of previous elements and at the same time lays a foundation for subsequent elements of study (Piaget, 1973, p.31). Teachers must understand that Piaget is primarily concerned with instruction that goes beyond memorized facts or skills. With a comprehensive knowledge of characteristics of concrete and formal operational thought, teachers will recognize various levels of student thinking within the broad range of mental development. One method which will provide students with activities that require logical thinking is to allow them to choose their own investigations. Initially, investigations would be simple, using tan...
