The main aims of this study were to observe the language development of individuals with Down Syndrome over five years, and to investigate the role of phonological memory in this development. The dataset includes information on the assessment of language, memory and nonverbal cognitive abilities of 30 individuals with Down Syndrome at two points in time, separated by five years. The assessments covered in the data include receptive vocabulary, grammar comprehension, non-word repetition, digit span, Kaufman assessment battery subtests - face recognition, hand movements, triangles, reading decoding, reading comprehension. For further information, please see documentation.