Typical and atypical development of elementary school basic numerical skills: Longitudinal study

Processing of numbers and numerosities has been
identified as a central component underlying arithmetic
development. Deficits in this domain are assumed
to be causally related to dyscalculia. Up to
date, empirical evidence comes mostly from cross
sectional studies, while longitudinal evidence is
scarce. The present study investigated the developmental
trajectories of symbolic and non-symbolic
numerical processing in 42 dyscalculic and 42 typically
developing children during the elementary
school years. Basic numerical processing skills
(non-symbolic comparison of magnitudes, symbolic
comparison of one- and two-digit numbers, physical
comparison, dot counting, number line estimation)
were assessed five times (beginning and middle of
Grades 2 and 3 and beginning of Grade 4). Developmental
changes concerned mainly the efficiency of
numerical processing while the overall pattern of
numerical processing was consistent across the study
period. Results also confirmed earlier findings that
dyscalculic children show generally less efficient
number processing reflected by specifically prolonged
response times. Furthermore, their symbolic
distance and compatibility effects appeared to be
more distinct than among their typically developing
peers. No major qualitative differences were observed
for the priming-distance effect for symbolic
number comparison and for non-symbolic numerical
processing, i.e both groups showed similar subitising
and counting patterns as well as a stable non-symbolic
distance effect from second grade on. Overall,
results suggest that the integration of two-digit numbers
as well as conscious numerical decisions based on
symbolic representations pose a particular challenge
in dyscalculia.