This study tested the hypothesis that individuals with dyscalculia have an order processing deficit. The ordering measures included both numerical and non-numerical ordering tasks, and ordering of both familiar and novel sequences was assessed. Magnitude processing/estimation tasks, and measures of inhibition skills were also administered. The participants were 20 children with developmental dyscalculia, and 20 children without maths difficulties. The two groups were closely matched on age, gender, socio-economic status, educational experiences, IQ and reading ability. The findings revealed differences between the groups in both ordering and magnitude processing skills. Nevertheless, diagnostic status was best predicted by order processing abilities.