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When numbers
just don’t add up
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 math difficulties,
say psychologist Michèle Mazzocco of
the Kennedy Krieger Institute in Baltimore 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
schoolchildren. Dyscalculia is defined
In one test, ninth-graders with dyscalculia had trouble determining whether
more blue or yellow circles were present in arrays of dots briefly flashed on
a computer screen.
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 schoolchildren
tested annually since kindergarten. By
third grade, kids with a math learn-
ing 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.
Mammoth etching found
An engraving of an Ice Age mammoth on a fossil bone could
be the oldest drawing in the Americas. Mammoths disappeared from eastern North America 13,000 years ago, so
the etching must be at least that old, says a team led by
anthropologist Robert Speakman of the Smithsonian Institution’s Museum Conservation Institute in Suitland, Md.
The team’s analyses indicate that the bone and etching are
ancient. The bone itself, found by an amateur fossil hunter
in Florida, comes from a mammoth, mastodon or giant sloth.
Speakman’s team does a “reasonable job” of showing that
the engraving is genuine, says archaeologist David Meltzer of
Southern Methodist University in Dallas. But the ;nd can’t be
dubbed the oldest American art without direct dating evidence,
Meltzer says. Replacement of the original bone by minerals
prevents DNA extraction or radiocarbon dating, the
scientists explain online June 12 in the Journal of
Archaeological Science. —Bruce Bower
