Problem size and mentally retarded children's judgment of commutativity.

The effects of problem size on judgments of commutativity by 51 moderately and mildly mentally retarded students were investigated. The task required subjects to judge whether commuted addition problems (e.g., 5 + 2 and 2 + 5) and noncommuted problems (e.g., 5 + 3 and 5 + 0) would have the same or different sum. Small problems had addends of five or less; large problems had at least one addend greater than five. The subjects' responses to the commutativity task were highly consistent across the two problem sizes. Results indicated that many retarded students who are given computational practice recognize the general principle that addend order does not affect the sum.