Two experiments which investigated the young child's ability to deal with multiplicative classes and relations (considered behavioral indices of concrete operations thought) in double series and cross class matrices are described and discussed. In the initial study, 160 children from preschool through grade 2 received six matrix subtasks (reproduction and transposition subtasks of cross classification, classification seriation, and double seriation) in one of six orders of presentation (the reproduction subtask always preceded the transposition case for a given matrix). The second experiment followed much the same design as the first, except that the class/series matrix was not used and stimuli for one cross class task were rearranged so that neither dimension was seriated across rows or columns of the matrix. Results, conclusions, and methodological problems of each experiment are discussed in detail. It was concluded that the pattern of lesser general difficulty for multiple relations contrasted with multiple classification concepts was subtantiated in these experiments (and other experiments (and other experiments also discussed) and that the original structural synchrony conclusions of Inhelder and Piaget need further examination. (ED)