It's the second day of school in Chaparral High School, a day assistant principal Todd Peterson calls "the second happiest day in the world for all the kids."

"They're measuring everybody up and they're making the decisions, one, if they like the teacher, and two, if they like the class," says Peterson, who leads the Las Vegas school.

These measurements can be critical: Early first impressions dictate who comes to school and how often, a question that influences who graduates, who goes to college and, ultimately, who gets a job. Students who miss 20 days of school have a 20 percent chance of dropping out, research shows.

That's why two years ago, advocates and experts funded partially by the Bill and Melinda Gates Foundation formed the "Get Schooled" foundation to raise awareness about chronic absenteeism, and to stress to families and students the importance of attending school consistently.

In the spring, the foundation released a report chronicling how often students miss school. Conducted by Johns Hopkins University professor Robert Balfanz, it found that between five and seven million students are chronically absent.

Chronic absenteeism -- defined as missing at least 10 percent of all school days -- is prevalent among high-poverty students, but common among all racial and socioeconomic groups.

"This is how poverty impacts kids' performance in school," Balfanz said when the report was released. "They have to get their sister to school, and that makes them late, so they just pretend to be sick rather than getting in trouble. Or they need to earn money to help the family. Or there's gang violence they're avoiding."

Now, Get Schooled is releasing a report that tries to flesh out the question of why students skip school. "We decided after that study, we needed to dig a little bit deeper to understand why so many students were missing so much school," explained Marie Groark, Get Schooled's executive director.

According to that report, released Wednesday, titled "Skipping to Nowhere: Students Share Their Views About Missing Schools," students skip school primarily because they're bored. "We want our kids to be happy in school, but it's not at that point where kids are able to pick their teachers and their subjects," said Peterson. "There are requirements and things you have to do in order to receive a high school diploma."

Get Schooled commissioned Hart Research's Geoff Garin to lead a team that conducted 516 interviews in 25 cities in June with students who reported skipping school a few times a month or more. When asked why, 49 percent said "school is boring." The next most important reasons were "classes or subjects I don't like," "more fun spending time with friends outside school," and school's early start-time. Sixty-five percent of students who ditch said that when they're missing school, they're hanging out with friends; 36 percent are sleeping.

Many reported their absences were unnoticed. "The perception of students is that it's far from certain that adults will know that they're missing school," Gorin said. Thirty-two percent reported teachers often don't notice when they skip, and 42 percent reported that parents often don't notice.

It's harder to detect absenteeism as class sizes swell to 40 students, Peterson said. "We run into the issue of whether teachers notice," he said. "It takes you a week to recognize and learn people's names, and realize that somebody's not there."

Students said that they might skip less school if they saw "a clear connection between the classes I take and the job I want," if the consequences of skipping were clearer, and if teachers seemed to care about their performance more.

New York City found that 200,000 of its students have missed a month or more of school, said Leslie Cornfield, who heads Mayor Michael Bloomberg's truancy task force.

"You can't attack the dropout-crisis in New York City ... without focusing early on in the pipeline when kids stop showing up," she said.

To combat absenteeism in the nation's largest school system, the city has started providing celebrity wake-up calls featuring the likes of Magic Johnson, and mentors who encourage kids to go to school. It will soon debut its newest weapon: MetroCards that have, "It's 9 a.m., do you know where your child is?" written on them.