Bakersfield, Calif. -- More than 4 million children in the United States have been diagnosed with attention deficit hyperactivity disorder, known as ADHD.

The symptoms of ADHD -- lack of attention, impulsivity, and difficulty staying on task -- can make schoolwork challenging for kids with the disorder .

Children with ADHD tend to get lower grades, are more likely to be held back a year, and have a higher dropout rate.

But new research from UC Berkeley finds that treatment with drugs such as Ritalin may help kids with ADHD perform better in school.

A study of nearly 600 children with ADHD showed that those who received stimulant medication scored about three points higher in math and more than five points higher in reading.

Experts said the medications help kids focus enough to use skills such as self-control and planning.

However, even kids receiving drug treatment lagged behind their peers academically, so researchers recommended parents and teachers give children individualized help -- including tutors if needed -- to keep them up to speed.