Simple mental addition in children with and without mild mental retardation

The speeded performance on simple mental addition problems of 6- and 7-year -old children with and without mild mental retardation is modeled from a pe rson perspective and an item perspective. On the person side, it was found that a single cognitive dimension spanned the performance differences betwe en the two ability groups. However, a discontinuity, or "jump," was observe d in the performance of the normal ability group on the easier items. On th e item side, the addition problems were almost perfectly ordered in difficu lty according to their problem size. Differences in difficulty were explain ed by factors related to the difficulty of executing nonretrieval strategie s. All findings were interpreted within the framework of Siegler's (e.g., R . S. Siegler & C. Shipley, 1995) model of children's strategy choices in ar ithmetic. Models from item response theory were used to test the hypotheses . (C) 1999 Academic Press.