The development of functionally similar and dissimilar operations of exclusion

Of Piaget's 16 operations of binary propositional logic, 5 concern exclusion. These 5 were classified into 2 operations of varying the independent variable, 2 of holding the independent variable constant, and tautology. The use of these 3 sets of operations and of levels of thought (concrete through formal) was assessed in 33 fifth graders, 27 sixth graders, and 31 seventh graders. Subjects' levels of thought were significantly affected by their grade. However, their use of the operations of exclusion was not. Instead, as predicted, formal operational and transitional subjects differed in their use of dissimilar operations. A proportionally greater number of formal operational subjects used the operation of varying the independent variable, whereas a proportionally greater number of transitional subjects used the operation of holding the independent variable constant.