Lisa Servon remembers her family’s bank, Pulaski Savings and Loan, as a routine stop during errands on Friday afternoons or Saturday mornings. It was where her parents deposited their paychecks, and where she opened her first savings account at 7 years old.

But banking has changed dramatically in the years since, says Servon, a professor of city and regional planning in Penn’s School of Design. Banks are bigger and more expensive to use, and cater to those who simply have more money. As a result, more and more people, from middle class families to millennials, are using alternative financial services, including payday lenders, check cashers, and informal borrowing groups.

Servon has a background studying urban poverty, community development, economic development, and issues of gender and race, and set out in her new book, “The Unbanking of America,” to understand why people are opting out of banks and using alternative services—some of which have been heavily criticized by consumer watchdog groups.

“I don’t really get why people would be using them if there wasn’t a good reason,” Servon explains. “My own work in poor communities had led me to believe people make good decisions with their money, especially if they don’t have very much.”

As part of her research, Servon worked at RiteCheck, a check cashing store in the South Bronx, and Check Center, a payday lender in Oakland, Calif. Initially, Servon says she thought of check cashing stores as places that preyed on their customers, usually the poor and working poor. But she soon found the issue was more complicated.

“Joe [Coleman, president of RiteCheck] made this very compelling argument about why he felt he was providing services in communities where banks were not serving the people there,” Servon says. “It stuck with me.”

She writes that customers continue to use check cashing places in part because fees are clearly spelled out up front. RiteCheck’s customers vary, too: Some have grown up using these services, while others have been pushed out of the banking system and feel they can’t afford to keep their money in a bank.

“When I was growing up, banks made most of their money from interest income,” Servon says. “That changed [partly] because the interest rates became more volatile and banks needed to think about a more stable way to make money.”

Banks discovered that fees on everything from overdrafts to ATM transactions were a way to turn massive profits. Debit resequencing, for example, is a practice at big banks that processes withdrawals in a way that causes balances to fall faster, which increases the chance of hitting customers with overdraft fees.

Regulations, including the Glass-Steagall Act of 1933, which separated commercial banks from the investment business, have been mostly overturned and picked apart, says Servon, and the size of the major banks makes them nearly impossible to regulate.

“There’s a level of real distress out there,” Servon says. “Banks are more reliant on fees, which makes consumers feel like they’re not well-treated.”

These practices—along with the trappings of credit cards—have created a sizeable group of people who are disadvantaged by the system, Servon writes, including millennials and middle class families.

“The rug has been pulled out from under the American workers,” Servon says. “For my parents, they could get jobs that would allow them to ... build assets. That is not as true anymore. It’s much harder.”

As she writes, the “new” middle class lives in a state of perpetual financial uncertainty. Nearly half of Americans live paycheck to paycheck. In the past few decades, productivity has increased while wages have either flattened or declined. And, she notes, millennials—people in their 20s and 30s—largely believe it was easier for their parents to achieve the American dream.

As things like credit card interest rates rise—to 16 percent, on average—greater numbers of people have turned to other places when cash runs short, including payday lenders.

As Servon found, these loans are sold as “quick fixes,” but customers end up rolling them over, which causes fees to dramatically increase, or after repaying, immediately take out another loan, which is essentially a rollover in all but its name. With payday loan annual percentage rates (APR) between 300 to 600 percent, this option penalizes consumers. But, as Servon says, it is understandable: A bank overdraft charge would be equivalent to a 5,000 percent APR.

Some people have chosen to save and borrow under the radar in rotating savings and credit associations, or ROSCAs. The arrangements, Servon writes, rely on trust between members and networks within communities.

Ultimately, Servon says we need to remove “value judgements” on people’s financial decisions. She also has suggested people be their own watchdogs and explore credit unions, and local and community development banks as alternatives to big banks.

“I tried to write the book in a way that follows my own learning and journey,” Servon says, adding, “this is an issue that affects many of us.”