It's not unusual for a child to have a tough time with math homework now and then. But if he has problems with numbers or low math test scores yet does well in other subjects, he could have a math learning disability called dyscalculia.

It's a brain-related condition that makes basic arithmetic hard to learn. It may run in families, but scientists haven't found any genes related to it.

Up to 7% of elementary school students have dyscalculia. Research suggests it's as common as dyslexia -- a reading disorder -- but not as well understood. In fact, kids and parents sometimes call it “math dyslexia,” but this can be confusing because dyscalculia is a completely different condition. Your school or doctor may call it a “mathematics learning disability” or a “math disorder.”

It can be associated with attention deficit hyperactivity disorder (ADHD) -- up to 60% of people who have ADHD also have a learning disorder, like dyscalculia.