# Math disability tied to bad number sense

Problems estimating quantities may underlie arithmetic cluelessness

By Bruce Bower

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.

Mazzocco’s new findings coincide with results from an ongoing study of more than 300 Missouri school children tested annually since kindergarten. By third grade, kids with math learning disability display several types of thinking hitches, says psychologist and investigation director David Geary of the University of Missouri in Columbia. In some cases of dyscalculia, youngsters have trouble gauging whether one set of items is more numerous than another. Others can’t estimate the number of items that they briefly see, quickly forget verbal information, can’t hold related pieces of information in mind or struggle in all of these areas.

“We’re trying to isolate different cognitive deficits that can result in math learning disability,” Geary says.

Mazzocco’s group studied 71 ninth-graders whose math abilities had been tested annually since kindergarten. Students completed two quantity estimation tasks. In one series of trials, participants saw an array of blue and yellow dots flash for a fraction of a second on a computer screen and indicated whether more blue or yellow dots had appeared. In other trials, students saw nine to 15 yellow dots flash on a screen and estimated how many dots were shown.

Students with dyscalculia, defined by the researchers as those whose math achievement scores fell within the lowest 10 percent of scores for their age, made substantially more mistakes comparing and estimating quantities than their peers did. That disparity remained after accounting for reading and memory problems among kids with dyscalculia.

Mazzocco and her colleagues previously found that the ability to estimate approximate quantities without counting generally improves during childhood and is related to math achievement (*SN: 9/27/08, p. 10*).

No scientifically validated interventions are available to combat dyscalculia or to bolster children’s number sense. Investigations now are focusing on computer games designed to foster basic math operations and quantity-estimation skills.