An unprecedented $10 million gift to Punahou School is expected to help 150 more families over the next five years afford an education at the state’s largest single-campus private school, and advance Punahou’s long-standing goal to increase access for qualified students.

The donation, from an alumna who wishes to remain anonymous, is designated for need-based assistance.

This school year, 579 students, or 15 percent of the student body, are receiving financial aid from the school, with the average need-based award at $9,300 toward tuition of $22,050. Punahou wants to grow that number to at least 20 percent, or to 750 students, over the next five years. Nationally, 21 percent of a private school’s students receive financial aid on average, according to the National Association of Independent Schools.

“It’s extraordinary,” Punahou President Jim Scott said of the gift in a recent interview. “To have it go to financial aid, which helps us support a major priority for the school, is thrilling. And really, it didn’t have a lot of strings, other than to be able to attract talented kids, regardless of their financial circumstances, who can benefit from and contribute to a Punahou education.”

The infusion of funds, he said, will mean that Punahou can provide the full demonstrated need for families requiring assistance. That does not equate to a full-ride scholarship, which officials say “virtually no” student receives. Families are expected to “reasonably” contribute toward a student’s education.

“We’re able to say that we can now meet 100 percent of a family’s calculated demonstrated need,” or the gap between what a family can afford and the cost of tuition, Scott said. “The aspiration is not new, but the ability to do it is new. This allows us to confidently and boldly go to the Hawaii community and say, ‘You can afford to attend Punahou.’”

Kathryn Nelson, vice president for institutional advancement at Punahou, said the donor was interested in the impact of financial aid on the school’s admissions philosophy.

“We can say that we’re need-blind, meaning that we read your application without knowing whether or not you’ve applied for financial aid,” Scott said. So-called need-blind admissions policies are typically only seen at Ivy League colleges with multibillion-dollar endowments.

Donovan Sabog, who attended Punahou with financial aid from seventh grade until he graduated in 2014, credits his education at the school for “unharnessing his potential.”

“Put simply, without financial aid, I wouldn’t have been able to attend Punahou,” Sabog, 19, said in a phone interview from Yale University, where he is double-majoring in applied physics and history. “I always tell people that my parents really worked hard to send me to Punahou, but that only went so far. It’s really the generosity of donors, like this one, that made Punahou a reality for me and every other student on financial aid.”

Sabog previously attended a public school and a small private school in Central Oahu but said he found school “to be easy and not interesting.” He finally asked his parents about switching schools.

“I knew that I wanted something more, but it was really the financial side of things that stopped me from even mentioning it to my parents,” he recalled, describing his family as in the average middle class. “We just really took a leap of faith and luckily I got admitted and the school provided a generous financial aid package that made Punahou a reality for me.”

With the aim of creating a multiplier effect, most of the anonymous gift — $8 million — has been set aside to match contributions of donors who establish endowments of at least $25,000 to support financial aid at Punahou. Forty funds have so far been established by a mix of individuals, families, alumni, faculty and staff.

Lesley Brey, a financial planner, and her husband, Dr. Randy Kam, a dentist, both received financial aid as students at Punahou. The couple, who sent their two children to the school, donated $25,000 to the cause.

“It is a stretch,” Brey said, “but we get letters every year from the kids who are beneficiaries of my grandfather’s endowed scholarship fund (at Punahou) and they are so inspiring. I cannot express how neat it feels when you read those letters. Especially once you’ve been through that. You realize what an advantage you get by being surrounded by people who are driven, and if you can give that to kids who would otherwise not have that opportunity, it gives you chicken skin.

“Somebody did this for me 40 years ago, and they didn’t know who I was,” she said.

Under Scott’s leadership, the number of students receiving financial aid has grown by 86 percent from 312 awards in 1994-95 to 579 this year. The school’s annual financial aid budget has increased more than fivefold, from less than $1 million to more than $5.3 million over the same time period.

Financial aid data show the school assists a wide socioeconomic range of families. The annual household income brackets with the highest number of awards are between $70,000 and $90,000.

Punahou officials say the school’s financial aid program is driven by its mission and educational goal of fostering a student body that is economically, ethnically, culturally and intellectually diverse.

Emily McCarren, principal of the high school grades, said that a diverse learning environment is critical to preparing Punahou students for the future.

“Having a community of people from diverse backgrounds elevates everything,” she said. “Diverse perspectives are key to understanding the world. We think it’s not just a nice thing to do for students receiving financial aid, but essential to continuing to support a strong learning community.”