# Math disability tied to bad number sense

## Problems estimating quantities may underlie arithmetic cluelessness

Math doesn’t add up for some kids, and a weak number sense may be partly to blame.

An evolutionarily ancient ability to estimate quantities takes a big hit in children with severe, instruction-resistant math difficulties, say psychologist Michèle Mazzocco of the Kennedy Krieger Institute and Johns Hopkins University and her colleagues.

In contrast, below-average, average and superior math students estimate amounts comparably well, the researchers report in a paper published online June 16 in *Child Development*.

“It’s possible that developmental routes to mathematical learning disability share a core deficit in numerical estimation,” Mazzocco says.

Math learning disability, or dyscalculia, affects an estimated 5 to 7 percent of school children. Dyscalculia is defined as consistent, extremely low scores on math achievement tests. Causes of this problem remain poorly understood.