Counting by children with Down syndrome.

Children's understanding of one-to-one, stable order, and cardinal principles was tested through error-detection and self-performance counting tasks. Gelman's modified counting task was used to test understanding of the order irrelevance principle. There were no significant differences between the mean task scores of 15 children with Down syndrome and 15 preschoolers with similar revised Peabody Picture Vocabulary test (PPVT-R) scores (mean age equivalent, 4 years, 7 months). Partial correlations showed several significant associations between counting principles and PPVT-R that were independent of chronological age. The results support the view that counting by children with Down syndrome can be guided by counting principles and that developmental level rather than the syndrome is associated with counting behavior.