Teaching is hard. No wonder 13 percent of the nation's 3.4 million public school teachers either change schools or quit the profession every year. Understanding the difficulties urban teachers face, many believe those educators in particular aren't paid enough for all they do. That sympathy has helped dampen criticism of Philadelphia teachers' refusal to agree to contract concessions.

The estimated teacher attrition rate in U.S. schools has doubled in 15 years. In some urban districts, teacher and student dropout rates are almost identical. Both new and veteran teachers are leaving - among them Maria Ciancetta, who quit in June after seven years as a Philadelphia teacher.

Ciancetta told The Inquirer's Kristen Graham that she felt called to become a teacher because her mother was an educator. But at Franklin High School, she lacked supplies, had crowded classes, and was tasked with teaching algebra to students with third-grade-level math skills. Discipline was a constant problem, Ciancetta said, because students knew they were getting an inferior education. "They don't verbalize it," Ciancetta said. "They act on it. They run the halls. They smoke in school. They cut class."

The high attrition rate among teachers not only makes it harder for schools to achieve academic consistency; it costs them money. The Alliance for Excellent Education says schools spend about $2.2 billion annually to recruit, hire, process, train, and orient new teachers. It found that Pennsylvania spends $31 million to $67 million a year on teacher attrition costs, while New Jersey spends $28 million to $62 million.

There's no easy solution to the teacher dropout rate. In recent years, some of the blame for the annual exodus has been placed at the feet of teachers whose poor academic records suggested they never had the acumen to become good educators. But new data have changed that perspective somewhat. In fact, in 2008, new teachers had higher SAT scores than the average among college graduates in other fields.

Education schools have been criticized as well for not preparing prospective teachers to handle ill-equipped classrooms, discipline problems, and children who speak English as a second language. College courses should reflect what teachers will actually face. Ultimately, though, just as with training soldiers for combat, nothing can replace actual experience.

It's hard for soldiers to win when they're outmanned, poorly equipped, and lacking adequate support. The same goes for teachers under those conditions. That's what they have argued in contract negotiations, and they're right.

But sometimes being right isn't enough. With another deficit looming, the possibility remains that not only will the city's teaching conditions get worse, but more teachers will be laid off - if they don't quit first.