My nephew and niece are in 1st grade and kindergarten, respectively -- and they're still at a point where school is exciting and fun.

But what kid hasn't had a "I hate school" moment -- or moments -- and refused to go to school? The Wall Street Journal reports on extreme cases known as "school refusal behavior."

These are the kids who may be absent for weeks or months. Some may cry or scream for hours every morning in an effort to resist leaving home. Others may hide out in the nurse's office. Some kids who miss school are simply truant—they'd just rather be doing something else. And sometimes there are genuine reasons to fear school, because of bullying, for example. But in about two-thirds of cases, a psychiatric problem, most commonly an anxiety disorder, is the cause, according to research led by Christopher A. Kearney, professor and director of clinical training at the University of Nevada, Las Vegas.

As the story notes, this can be debilitating for the whole family. And left untreated, these kids can fall behind academically as well as suffer long-lasting effects as adults, such as depression.

According to the article, children can overcome school-refusal behavior and the anxiety disorders that often underlie it through cognitive behavioral therapy, in which patients learn to change their behavior.