Nearly halfway into the school year, Harding Middle School has six teaching vacancies - the same number it has had since September.

Some open positions have been filled along the way, longtime Harding teacher Bernadette MacDonald said, but others have cropped up, leading to overstuffed classes and an atmosphere that "makes it harder and harder to stay," even for veterans.

"We had one teacher quit to go sell tacos at a taco truck," said MacDonald, a sixth-grade teacher at the Frankford school. "He said he would rather do that than work at Harding."

Always a tough-to-staff system, the Philadelphia School District is having particular challenges finding and retaining teachers this year. As of Friday, there were 162 vacancies - up from 107 at this point last year, and 39 in January 2014.

With 8,000-plus teachers and 218 schools systemwide, the 162 unfilled jobs mean that about 2 percent of teaching jobs remain open. But that obscures the fact that the absence of a permanent teacher - and, most often this year, substitutes to fill in - robs students of continuity and, in some cases, high-quality instruction for months at a time.

Superintendent William R. Hite Jr. said it is one of the biggest challenges he faces.

"We're not at a place where I'm satisfied with our ability to fill vacancies, but it's not for a lack of effort," Hite said. "This is our most important work."

The school system has hired 1,050 new teachers since July, Hite noted - hundreds more than in previous years, when open jobs were mostly filled with Philadelphia teachers who had been laid off and could be recalled. But it has also seen considerable turnover, with potential job candidates likely turned off by a three-year contract dispute and an acute financial crisis.

Until Gov. Wolf released some emergency school funding at the beginning of the month, Hite wasn't sure he'd be able to keep schools open past Jan. 29.

"That doesn't communicate a level of stability to potential candidates," the superintendent said.

Teachers' union president Jerry Jordan laid responsibility for the staffing crisis squarely on the district.

"I have never seen anything like this; it is just astounding that this is even allowed to happen," Jordan said. "When you don't have good conditions, people will choose to work at the taco truck rather than work in Philadelphia schools. We have children deserving to be educated - this is a huge equity issue."

At Wagner Middle School in West Oak Lane, six teaching jobs are vacant - all in major subjects. That means that some classes have split, with seventh graders placed in rooms with eighth graders, and some teachers have taken on double loads in a single class period.

"We've rearranged the schedule so people can get a semblance of an educational experience," said Brad Berry, a sixth-grade literacy teacher. "But keeping people motivated is hard to do."

Berry teaches one double class "because there's no other place for the kids to go." An aide helps with crowd control.

The setup, he said, is less than ideal.

"You end up giving the kids busy work sometimes, honestly," said Berry, a district veteran. "I've never seen a year with this many vacancies."

Ramona Lewis, a teacher at Beeber Middle School in Overbrook, has 46 students in one class and 47 in another. Those numbers are down, but only slightly, from where they were in September. The school was supposed to get relief in October, staff said, but no teachers ever arrived.

"I don't even know what type of fire codes we're violating with the overcrowded rooms," she said. "I cannot walk up and down the aisles, and I need six more desks."

Lewis is a seasoned teacher, and can generally manage the crowd, but said, "I'm constantly raising my voice. I fear sometimes that I might be getting some kind of condition on my vocal cords."

Beeber has less than 200 students and is slated to close in June. Lewis wonders whether higher-ups have already given up on the school; she said she has no reason to believe anything will change by the end of the year.

Research is clear, said Jonathan Supovitz, a professor in the University of Pennsylvania's Graduate School of Education: class size matters.

"The poor unfortunate teacher with 47 students is probably doing a whole lot of large-scale, whole-class kind of stuff, which doesn't get to the individual needs of the kids at all," said Supovitz. "This is not a great situation for that teacher, or for those students."

Indeed, said Lewis - she can't conduct any small-group instruction, or oversee innovative lessons or project-based learning. Beeber, too, has a high percentage of pupils with special needs and federally mandated individualized education plans.

"The students are not getting everything that they should be," Lewis said. "There's just not enough staff members there."

Beeber has a supportive principal, Lewis said, but his hands are tied.

"In my 22 years, I have never been handed a roll sheet with 50-plus student names on it," she said. "That never would have happened in the past."

Jordan, the Philadelphia Federation of Teachers president, said that, in the past, district human-resources staff maintained "eligibility lists" of qualified candidates with all paperwork in order so that when vacancies cropped up, as they often do in a large urban system, teachers could be placed quickly.

That seems to have fallen apart this year, Jordan said.

Cuts to central-office staff mean fewer recruiters on the ground than in past years, said district spokesman Fernando Gallard, but the real issue is a competitive market, he said.

The school system made blanket job offers to all qualified December graduates of local education schools, he said. Two hundred teachers graduated from Temple and West Chester Universities; of those, just 43 responded to Philadelphia's job offer - and only 17 accepted.

Good human-resources teams know what their hiring season is, anticipate vacancies, and overstaff to cover blind spots, said Naomi Wyatt, the district's chief of staff.

The district had funds to do none of that, she said.

"When you have no extra dollars, you can't overhire," Wyatt said. "Budget shortage has a real implication for us, every day."

MacDonald, the Harding teacher, can speak to that. Harding "has always been tough," she said.

But this year has been tougher than ever, MacDonald said. The school has hardly seen a substitute position filled all term, and some midyear replacements lasted just a few weeks.

Years of budget cuts and working conditions that wouldn't be acceptable anywhere else, she said, have worn people down.

"The new normal is, 'You don't have it, whatever it is,' " MacDonald said. "I don't remember the last time we got textbooks. We don't have enough books for the kids, and forget workbooks - you're lucky if you have one to make copies from."

MacDonald, whose smallest class is 35 students - still over the contractually mandated class maximum of 33 - has had it.

"I'm taking early retirement," she said. "I'm going to take a penalty, and I'm going to work at Costco."

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