Texting. Twittering. Long sessions with the MP3 player. The trappings of modern life can be so distracting that kids can't focus on things that really matter - like schoolwork.

"We have super-connected electronically but have been disconnecting interpersonally," says Dr. Edward Hallowell, author of several books on ADHD including "Superparenting for ADD." "It can be hard to tell ADHD from what I call a 'severe case of modern life.'"

Some kids are anxious because they're worry that a bully is waiting for them in the bathroom or after class. In the classroom, anxiety can look a lot like ADHD.

Too much caffeine can make kids so jittery they look hyperactive. "If you have a Mountain Dew for breakfast and three cokes for lunch, you are going to be wound up," says Dr. Hallowell.

Perfection makes it hard to get things done.

"A kid who is 'perfectionistic' may be unable to move on to something else" says Dr. Larry Silver, clinical professor of psychiatry at Georgetown University Medical Center in Washington, D.C. and the author of "The Misunderstood Child."

He says it's hard for kids to complete assignments if they are too busy "lining up pencils and making sure the paper is in the right place."

Some kids who seem distracted are just anxious. Some actually suffer from a diagnosable anxiety disorder, says Dr. Silver.

Some kids have trouble focusing on schoolwork simply because they are too young, according to recent research.

Depression can cause behavior that looks a lot like ADHD. Children suffering from so-called "agitated" depression may be just that - too fidgety to focus. Those with psychomotor depression may seem inattentive.

Is there a new member in the family? Has a family member or close friend moved away or died? "Stressors" like these can cause kids to seem highly distracted, says Dr. Silver.

An overactive thyroid gland can cause restlessness and irritability. An underactive thyroid can make kids lethargic. Thyroid disease strikes kids of all ages, but is most common in high schoolers, says Dr. Silver.

A child whose blood sugar level is out of whack might seem lethargic - or overly energetic.

Kids with dyslexia or another learning disability might find schoolwork so challenging that they simply give up. Rather than apply themselves, they sit quietly and doodle - or fidget nervously. Either way, they may look as if they have ADHD.

How can a teacher tell the difference between a child who ignores what is being said and who simply can't hear well? It's not always easy. Some children branded inattentive by their teachers actually have hearing loss.

A child who seems distracted or inattentive in class might simply be bored. Maybe the work is too easy. Or maybe it's so difficult that he/she becomes frustrated and simply gives up.

Kids with autism spectrum disorders, including Asperger's syndrome, may be so focused on what's going on inside their minds (thoughts of dinosaurs, space travel, etc.) that they can't focus on what's going on in the classroom.

Maybe a child seems spacey not because of ADHD but because he/she is stoned. To take one example, marijuana can make kids apathetic or sleepy - and can cause memory problems that look a lot like inattentiveness.

Some kids have trouble focusing on schoolwork simply because they are too young, according to recent research.

Some types of epilepsy cause seizures so brief and so subtle that they aren't recognized for what they are. But these so-called "petit mal" seizures can hamper a child's ability to pay attention, says Dr. Hallowell.