That's when classwork gets harder and they fall behind. The teacher, bent on enforcing No Child Left Behind, can't afford to wait on the one who's actually being left behind.

They start missing days here and there. Days turn into weeks, months, years. To the point of no return.

You can guess where too much time out of school leads.

No good. Or worse.

It's a sad and all-too-familiar tune - a requiem for the high school dropout in Philadelphia.

That's pretty much the story Joshua Smith and Darlene Keels told me about their path to leaving school behind.

Sour notes sung of academic struggle, teacher indifference, parent apathy, and lack of personal responsibility.

But unlike most, who never return to school, the good news is that Smith and Keels are now working toward getting their GEDs at the Southwest e3 (education, empowerment and employment) Center, which provides disconnected students a second chance. A chance to get their lives back on track, whether that means finishing high school or getting job training.

Their re-entry back into academia wasn't smooth. It took a crash landing - in the form of imprisonment - and a court-ordered assignment to e3 for both to realize they didn't want to be statistics, part of the 40 percent high school dropout rate in Philadelphia and nationally.

That's a rate so alarming that Mayor Nutter has vowed to cut it in half in five to seven years. He also has his sights on doubling the percentage of those with bachelor's degrees. (Only 18 percent of city residents have college degrees, which ranks Philadelphia 92d out of the 100 top cities.)

He's right to make it a priority. An uneducated adult population is a drain on taxpayers. And if we want to be a great city, we need to have an educated workforce.

But hearing Smith's and Keels' stories makes it clear that we have to understand the problem before addressing a solution. Some teens' issues are just too layered and complex to be fixed with a cookie-cutter answer.

Joshua Smith, an introspective 18-year-old with the furrowed brow of someone much older, told me his "dumb decisions" led to his eventually dropping out of Dobbins Tech in the 10th grade.

Dumb stuff, like punching out a fellow student and, he says, accidentally hitting a teacher as a ninth grader; landing on probation; then, the car theft that violated his probation and sent him to a juvenile facility for 18 months.

"Peer pressure," he says by way of explanation. "I was hanging with the wrong crowd."

But Joshua knows it was more than that. The middle of four kids, he would have behaved better if his father had been around, he says.

"He's locked up" for drugs, Joshua explains. "I haven't seen him since I was 11. They moved him, and then we moved and we lost contact."

His mother was on him all the time up to the ninth grade, he says, but then she started "working too much" and the pressure dropped off.

By 10th grade, "I was missing so many days, when I'd go to class the teacher sounded like, 'Blah-blah-blah.' I was so far behind in the work, they told me that I'd have to do at least five more years of high school."

Five years? Considering where his head was at, one was too many. "I thought, 'What's the use?' " he said.

Same with Darlene Keels.

"I was slow and didn't want to go to class," says the 17-year-old, so soft-spoken that it's hard to imagine her being suspended numerous times for fighting. "School started getting hard in eighth grade."

At Bartram High, "I was the kind who would tell a joke and disrupt the whole class because I was so far behind," she recalls. "Sometimes I was missing two weeks at a time."

She felt uncomfortable sharing her struggles with her guidance counselor. Or her own mother and stepdad, for that matter.

Darlene guesses her mom saw only one report card during her entire high school career.

"I would get to the mailbox before she would, or when she asked, I'd tell her I was on a different grading period," says the second-oldest of four siblings - soon to be six, after Darlene's mom gives birth to twins later this year.

After getting locked up for three weeks in October for fighting, Darlene realized she had to get it together. The judge gave her a choice: Either return to Bartram or enroll at an alternative school like e3. She chose e3.

"Being here, people encourage me," she says. They allow her to learn at her own pace.

And perhaps most important, they listen.

Now she has a plan: Earn a GED this year, go to Community College, then eventually transfer to Cheyney for a teaching degree.

Joshua has college plans, too. He likes culinary arts. Maybe he'll become a chef, he says. Meanwhile, he's landed two jobs through e3 - at a Burger King and a barbershop.

And he has some advice for anybody following his wayward path: "Think about your future and not about now. People used to tell me that, but I thought it was too late for me."

at ajohnhall@phillynews.com or at 215-854-4986. To read her recent work: http://go.philly.com/annette.