She was so financially stretched, she said, that she and her daughter often sneaked into her son’s high school football games free during halftime because she couldn’t afford the $6 tickets. (She proudly noted that her son, Charles, had made the All State football team.) As for her daughter Jer’Maya, who mimics Beyoncé’s every move on her mother’s iPhone, Ms. McCurdy said, “She’d love to take ballet and piano lessons, but there’s no way I can afford that.”

Having worked as a nurse’s aide for 15 years, Ms. McCurdy has been among the nearly 25 million workers in the United States who make less than $10.10 an hour — the amount to which President Obama supports increasing the minimum wage. Of those workers, 3.5 million make the $7.25 federal minimum wage or less.

And like many of them, Ms. McCurdy hasn’t been able to rely on steady full-time hours — she has often been assigned just 20 hours a week. Even if she worked full time year-round, her $9 hourly wage would put her below the poverty threshold of $19,530 for a family of three.

Climbing above the poverty line has become more daunting in recent years, as the composition of the nation’s low-wage work force has been transformed by the Great Recession, shifting demographics and other factors. More than half of those who make $9 or less an hour are 25 or older, while the proportion who are teenagers has declined to just 17 percent from 28 percent in 2000, after adjusting for inflation, according to Janelle Jones and John Schmitt of the Center for Economic Policy Research.

Today’s low-wage workers are also more educated, with 41 percent having at least some college, up from 29 percent in 2000. “Minimum-wage and low-wage workers are older and more educated than 10 or 20 years ago, yet they’re making wages below where they were 10 or 20 years ago after inflation,” said Mr. Schmitt, senior economist at the research center. “If you look back several decades, workers near the minimum wage were more likely to be teenagers — that’s the stereotype people had. It’s definitely not accurate anymore.”