(Non-)symbolic magnitude processing in children with mathematical difficulties: A meta-analysis.
Symbolic digit comparison speed—not the distance effect—is the reliable red flag for math difficulties.
01Research in Context
What this study did
The team looked at 45 studies on kids with math trouble. They asked: do these kids struggle with number sense tasks?
They compared two kinds of tasks. Symbolic tasks use digits like 3 vs 8. Non-symbolic tasks use dot pictures.
They measured both speed and the distance effect. The distance effect means people answer faster when numbers are far apart.
What they found
Kids with math difficulties were much slower on digit tasks. The effect was large.
They were only slightly slower on dot tasks. The effect was small.
Surprisingly, both groups showed the same distance effect. This means the problem is speed, not number sense itself.
How this fits with other research
Leng et al. (2024) extends these findings. They found autistic preschoolers also struggle on dot tasks. This shows the deficit appears across different neurodevelopmental conditions.
Leaf et al. (2012) used the same meta-analysis method for Down syndrome reading. Both studies reveal that basic skill speed matters more than strategy differences.
Herzog et al. (2026) tested computer math training for low performers. Their mixed results make sense now. If speed is the core issue, training must target fluent responding, not just accuracy.
Why it matters
Stop using distance effect tasks to screen for math risk. Instead, time how fast kids pick the bigger digit. A 30-second timed task beats fancy distance measures. If a child is slow on digits but okay on dots, flag them for math support.
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02At a glance
03Original abstract
Symbolic and non-symbolic magnitude representations, measured by digit or dot comparison tasks, are assumed to underlie the development of arithmetic skills. The comparison distance effect (CDE) has been suggested as a hallmark of the preciseness of mental magnitude representations. It implies that two magnitudes are harder to discriminate when the numerical distance between them is small, and may therefore differ in children with mathematical difficulties (MD), i.e. low mathematical achievement or dyscalculia. However, empirical findings on the CDE in children with MD are heterogeneous, and only few studies assess both symbolic and non-symbolic skills. This meta-analysis therefore integrates 44 symbolic and 48 non-symbolic response time (RT) outcomes reported in nineteen studies (N=1630 subjects, aged 6-14 years). Independent of age, children with MD show significantly longer mean RTs than typically achieving controls, particularly on symbolic (Hedges' g=0.75; 95% CI [0.51; 0.99]), but to a significantly lower extent also on non-symbolic (g=0.24; 95% CI [0.13; 0.36]) tasks. However, no group differences were found for the CDE. Extending recent work, these meta-analytical findings on children with MD corroborate the diagnostic importance of magnitude comparison speed in symbolic tasks. By contrast, the validity of CDE measures in assessing MD is questioned.
Research in developmental disabilities, 2017 · doi:10.1016/j.ridd.2017.03.003