This paper presents a study using a neo-Piagetian theory to analyze the micro-structure underlying Piaget's "control of variables" scheme. Data are presented which support the conclusion that young children are capable of acquiring and utilizing this scheme before they acquire Conservation of Weight, that is, providing (1) that the children are at least 7-8 years old; (2) that they are field independent and (3) that they have been exposed to previous situations in which an uncontrolled test was conducted and the ambiguity of the results was made apparent. The results are discussed with regard to Piaget's theory of development and the limitations of development on learning. (Author/CS)