"It hit me hard," said Greene, sitting at People's Emergency Center, a social service agency that works with people who have experienced homelessness. She has been pursuing her GED there since March. "I had a job that I felt was my passion and could not pursue because I didn't have a GED."
Since then, Greene said, she has tried many times to reconnect into the city's workforce, only to fall short for lack of a diploma. "No one would hire me without it," she said.
The trench between Philadelphia's job needs and the skills of its workforce is a tremendous challenge facing a city where 25 percent of residents live in poverty.
Until the 1970s, the city was a hub of manufacturing, a sector that employed one in four residents. Today, less than one in 20 holds such a job, according to a 2009 report by the Philadelphia Workforce Investment Board.
Based on educational attainment, more than half of adult Philadelphians are "unskilled," meaning they lack the literacy skills to compete in an increasingly knowledge-based economy, Mayor Nutter said this summer. As a result, about 550,000 residents are unqualified for 62 percent of the city's jobs.
"We're finding there is an absolute mismatch in the system," said Mark Edwards, president and CEO of the Philadelphia Workforce Development Corp., part of the mayor's plan to create a one-stop-shopping source for employers and employees. "People have had to retool with this 21st-century workforce."
Since Nutter came into office, he has set a goal to increase the number of residents with a four-year college degree, from 23 percent currently to 36 percent by 2015. Philadelphia is tied with San Antonio among the country's 10 largest cities in having the highest percentage of adults without a bachelor's degree or higher, according to census data.
Falling further behind in the city's jobs economy are the estimated 19 percent of working-age Philadelphians, or 194,000 residents, who never completed high school. Only 37 percent of them hold jobs, compared with 61 percent for residents with a high-school diploma and roughly 83 percent for those with a bachelor's degree or higher.
From the interaction among education, employment, and earnings nationally, the median wages of those without a high-school diploma come in at less than $11,000 a year. They are less likely to work full time year-round, according to a Census Bureau study released last week.
For Eric Johnson, making a living has been hard.
Johnson, 33, dropped out after 11th grade, drawn to his friends and fast money on the streets. He later worked meager jobs in fast-food, security, and construction, hamstrung without a diploma.
Johnson, father of a 6-year-old daughter, still lives with his mother in Southwest Philadelphia.
"I can't get the necessary jobs that I need to provide for my family," said Johnson. He applied for about 20 jobs in the last year without success.
"They ask me if I have a diploma, and I just tell them, 'No.' And that ends the conversation."
Johnson has been taking adult-basic-education classes at the National Comprehensive Center for Fathers. He wants to get his GED and become an electrician "for my family, my daughter, for myself. I want to make sure my daughter gets what I didn't get."
So far, writing has been his nemesis. He did not pass the GED exam last year, undone by punctuation and spelling, but has returned for refresher classes.
Those applying for jobs now face steep challenges, said Edwards, of the Workforce Development Corp.
"Employers are getting access to employees who are high-skilled at lower amounts of money," he said. "But at the same time, it's impacting the region in that lower-skilled workers find themselves out of work."
Providing the bulk of the city's jobs are hospitals, universities, and the hospitality sector, with jobs emerging in new media, technology, and alternative energy, said Robert Wonderling, president and CEO of the Greater Philadelphia Chamber of Commerce.
"The jobs of the future still require good old-fashioned reading, writing, and arithmetic," he said. "Those ingredients still apply."
At People's Emergency Center, the barriers to higher education and stable employment are on display. There, the mothers, on average, read at a fourth-grade level, said Malkia Singleton, vice president of social services. As for math, even those who have made it out of 11th grade are on a third-grade level.
"The impact is tremendous," said Singleton. "It boils down to, 'Now that my child is in school, I can't help them with their homework.' And economically, without extra education, you're pretty much going to stay in the same place."
For Greene, school had been a refuge from a troubled life, her mother hooked on drugs. But she dropped out of Strawberry Mansion High at 15, she said, after her family was evicted. Before long, Greene had a child of her own.
As a single mother with a young son, she strung together jobs, working as a cashier, a supermarket clerk, and then a security guard. For a while, she worked as a certified nursing assistant at nursing homes and hospices, continually reminded of her past.
Riding home on the bus one day, she struck up a conversation with a passenger in familiar scrubs - a nursing assistant at a hospital. With her high-school diploma, she earned almost twice Greene's $9 an hour.
"I felt so bad," Greene said.
Tragedy derailed her again in 2008 when her 23-year-old son was killed. Greene, brokenhearted, put off getting her GED, until now.
She came in thinking, "I might not be able to do this." Now, after passing four of the five tests - writing, social studies, science, and reading - she has started to believe.
The last test, math, is next week. It's an intimidating subject for her.
She also recently landed a part-time job, at a women's shelter. After she gets her GED, Greene wants to pursue a degree in social work.
She went to the center one day last month from her rent-subsidized home in West Philadelphia and sat in a class of 20. The day's lesson: percentages and word problems. She has a peer tutor, who recently obtained a GED after being laid off from his janitorial job.
At home, her two teens help her study.
"I told my son, 'For someone who says they don't like school, you seem to get this down pat,' " Greene said, then chuckled. "I just want to inspire them, for them to say, If she can make it, let me go ahead while it's easy."
Contact staff writer Kia Gregory at 215-854-2601, kgregory@philly news.com, or @kiagregory on Twitter.com.