Distinguishing two forms of inference (additive and general vicariance), this paper describes a procedure for assessing class vicariance that attempts to control potentially confounding effects of verbal comprehension. The term "class vicariance" refers to the inference that a class remains invariant under arbitrary dichotomous partitionings. Additive vicariance refers to inferences in which subclass structure is additive and involves no class multiplication. General vicariance refers to inferences in which classes are partitioned multiplicatively. A broader theoretical issue addressed by this research is that of whether additive and multiplicative operations on classes develop simultaneously or asynchronously. It is hypothesized that applying vicariance in the case of additive subclasses would be achieved earlier than applying it in the general case of multiplicative subclasses. A total of 72 children were tested individually on four additive and three general vicariance problems. Subjects ranged in age from 5 years to 7 years, 10 months. Findings support Piaget's interpretation of additive class vicariance as a distinct acquisition of the concrete operational period. Performance on these problems shows progressive development across the age range of 5 through 7 years. Clearly, though, children do not achieve consistent success on these problems even at age 7, and this is especially true for general vicariance problems. (RH)