Discussed are results of studies of the cognitive development of 2- and 3-year-old children which suggest that the mind makes gains in the ability to think as gains in language development are made. "Thinking" in this context refers to the judgments children made as they selected objects and maneuvered them into one arrangement or another. A study of forty 1- to 3-year-old children's spontaneous manipulations of a series of object sets (divisible into two classes of four objects each) indicated two major shifts in the children's conceptual structuring. The first shift in structuring, which was found to occur during the second year, involved the construction of explicit similarity or equivalence relations between discrete objects. Beginning at 12 months, children selecting same-class objects tended to manipulate one type of object throughout a task. Between 12 and 24 months children produced two-class groupings only by arranging one class at a time. The second shift in structuring, which occurred in the third year, involved a change in the procedure children used to construct two-class groupings. Half the 30- and 36-month-old children shifted between classes as they grouped items. It is concluded that age difference in manipulative procedure suggests a difference in conceptual strategy. Implications of the findings for Piagetian theory are discussed. (RH)