Research on 128 children is presented as evidence of the superiority of a new clustering measure (X) over a more traditional "chance clustering" measure (sigma) as a means of organizing material to be learned to facilitate recall. X is shown to meet three criteria for a measure of a developmental process: X is more highly correlated with recall…

Learning-disabled ninth-graders (n=58) completed a modified Piagetian isolation-of-variables task, and were compared to normally achieving ninth-graders and fourth-graders. Through cluster analysis, four different patterns of task approach were identified, representing normal performance, general conceptual disorder, specific developmental delay,…