On Monday her activism paid off, as 70,000 workers in San Jose enjoyed the nation’s single largest minimum-wage increase, a 25 percent raise from $8 to $10 an hour, amounting to a $4,000 annual bump in pay for a full time worker to $22,080.

“I never doubted for a minute we could make this happen,” said Castro, 28, who grew up in the agriculture-rich community of Gilroy, where her parents and at times Castro herself picked garlic, lettuce and other vegetables in fields surrounding the town.

Castro said that while putting herself through college in 2011, she worked at an after-school program with low-income children who would slip snacks into their backpacks because there wasn’t enough food at home.

Meanwhile in her sociology classes she was reading about how living on minimum wage leaves workers – especially those in one of the wealthiest regions of the country – in severe poverty.

“When I understood what was happening in our community, it started to really piss me off,” she said.

In her Social Action class, sociology professor Scott Myers-Lipton assigned everyone to create an advocacy campaign of their choosing. Castro and several classmates decided to take on the minimum wage.

“At some point during that semester it hit me that this was much more than a class project,” said classmate Leila McCabe, 31, who graduated and now works for a nonprofit. “But we were determined and now that it’s happening, it’s amazing, very emotional.”

The students started with a poll that found 70 percent of the community favored an increase. They later learned one in five local workers would be directly impacted. Then they asked Cindy Chavez, who heads the South Bay Labor Council, representing more than 90 unions, to join them.

“When you live in a place as expensive as Silicon Valley, the fact that people here are paid so little and still figure out a way to hang on by their fingernails here is just sort of astounding,” Chavez said. “We were very excited to take this on.”

In November, 59 percent of San Jose voters approved the raise, making it the largest city in the U.S. to date to raise its minimum wage. Voters in Long Beach and Albuquerque, N.M., also approved similar measures in November.

Nineteen states, including California, and other cities have raised their minimum wage above the federal level of $7.25. Congress is currently considering the Fair Minimum Wage Act of 2013, which would raise the federal minimum wage to $10.10 an hour by 2015.

California’s minimum wage is $8 an hour. San Francisco’s $10.55 an hour minimum wage, the highest in the country, took effect on Jan. 1.

Opponents in San Jose had argued that raising the minimum wage would cripple San Jose’s fragile economic recovery, causing employees to lose hours or even their jobs. On Monday, opponent Scott Knies, executive director of San Jose’s Downtown Association, said some businesses have already raised prices or cut hours.

Knies was trying make the best of it, launching “Earn ‘n Spend in San Jose,” a campaign that urges workers who benefit from the raise to keep their dollars local.

Nick Taptelis, owner of Philz Coffee, raised his wages to $10 an hour more than a month ago. He said he’s been surprised to find that happier workers mean better customer service, which in turn has brought more people into his bustling shop near the university campus.

Supporters of the wage increase gathered outside his cafe on Monday, chanting, “What time is it? It’s time for 10!”

Castro, 28, was beaming as her former professor patted her on the back.

“This was just a group of regular people, students at a university,” said Myers-Lipton. “We didn’t have a lot of political power, but this shows that regular folks can change economic policy in this country.”

Castro said her professor was “very smart and very inspiring.”

So what grade did she end up with?

“Actually I got a B,” she said. “He’s also a really hard grader.”