Two studies on cognitive performance in mentally retarded children are reported. In the first study, the Bayley Scales of Infant Development were administered to 56 mentally retarded children, aged 2 to 6, to determine the possibility of discerning subsets of items that form a developmental pattern of interrelated subscales, using the SCAMMO scale analysis. Three partially interrelated subscales emerged in the Motor Scale and five subscales in the Mental Scale, suggesting that mentally retarded children may follow a variety of possible developmental paths or partial paths that exhibit logical and/or psychological consistency and structure. The second study investigated Down Syndrome children's problem-solving strategies within a developmentally oriented theoretical framework. Four children aged 9-13 were required to reconstruct a lane of four slanted blocks in a motorway form board. Analysis showed that the Down Syndrome children may exhibit systematic problem-solving behavior in a complex multistep task and an increase of its efficiency due to active forms of regulation. However, the children showed perseverative tendencies, and their error monitoring routines were slow to develop. (Author/JDD)