Somerville Munt, a recent graduate of Fluvanna County High School in Palmyra, Va., said she was disappointed when she found out in March that she had been wait-listed by William & Mary.

“There’s basically no chance of me getting in,” she remembered thinking at the time.

About a week later, as she was scrolling through her email trying to plan her next step, Ms. Munt noticed a message from the Williamsburg, Va., school. It would guarantee her admission in spring 2022 if she spent her first semester studying abroad in a program offered through Verto Education, a for-profit company. She immediately signed up to study in Costa Rica, she said.

Facing record numbers of applicants and increased pandemic-related uncertainty over which admitted students will actually enroll, some colleges are finding new ways to ensure that their campuses take on the right number of students to start the year. Having students study abroad during their first semester, an experience that is usually advertised for upperclassmen, helps the schools meet their enrollment goals, take in more culturally aware students and broaden their geographical reach, some college admissions officers say.

Though some schools support students taking gap years, these new efforts are more proactive, urging wait-listed students to go away for a stretch and promising them a spot upon their return. Without enrolling in the study-abroad program, these students might not otherwise be admitted to the school.

The unusual path to admission is catching on after a year in which the number of applications submitted through the Common App, which is used for more than 900 schools, increased by at least 11%. Some schools, especially highly selective ones, saw an even bigger increase and longer wait lists.

William & Mary received almost 17,500 applications, up 23% from last year. About 37% of freshman applicants were admitted. It offered 4,700 people spots on the wait list, up from around 4,000 in 2019. It expects to admit a total of between 30 and 40 from the wait list, said Henry Broaddus, vice president for strategic initiatives and public affairs. In addition, the school expects to enroll about 100 students from its wait list for the 2022 spring semester after they spend the fall studying abroad.

“One thing that we included as an important feature for our enrollment growth strategy was to make a new point of entry for students in the spring semester,” Mr. Broaddus said.

Somerville Munt, a recent graduate of Fluvanna County High School in Virginia, plans to attend William & Mary after spending a semester abroad.

Photo: Fluvanna Sports Photography

Verto, a five-year-old startup, said it guarantees its students admission into at least one of its 65 partner schools across the U.S. after they spend a semester or more earning college credit by taking its courses abroad or in Hawaii. The schools that Verto feeds into—including Pace University, Catholic University of America and Oregon’s Portland State University—are a mix of public and private institutions and vary in selectivity and size.

A smattering of colleges offer their own alternative-admissions pathway through study abroad. Northeastern University offers some applicants who weren’t admitted in the fall a chance to complete a fall semester abroad through its own program before continuing their studies on campus.

Several other study-abroad programs offer college credit and are available to incoming freshmen. Those opportunities, however, are mostly for students who have already been admitted to a college. The University of Southern California offers its spring admits the opportunity to study abroad during the fall semester as a way to stay on track to graduate in four years.

William & Mary is among a handful of schools offering guaranteed admission specifically to its wait-listed students in the spring if they study abroad with Verto. The other partner schools agree to consider accepting participating students as transfers.

Verto charges the schools a fixed annual fee, said Mitch Gordon, Verto chief executive officer, who declined to disclose the amount.

A semester abroad through Verto costs students $15,000 to $25,000 depending on the location, and students may apply for federal financial aid. Mr. Gordon said it uses donor funds to provide need-based grants of $5,000 or $10,000 to students whose household income is below $125,000.

“ ‘One thing that we included as an important feature for our enrollment growth strategy was to make a new point of entry for students in the spring semester.’ ”

— Henry Broaddus, vice president for strategic initiatives and public affairs, W&M

Mr. Gordon said the company is tapping into an underserved student population including wait-listed students, those who need more admissions guidance to get into their top-choice schools, those who wish to have a more impressive college application and those who want to travel while earning college credit.

Over the past year, the company nearly doubled its roster of partner schools by adding about 30 schools to reach 65, and it forecasts signing up an additional 30 in the coming year, said Michael Kabbaz, Verto senior vice president and chief of staff. Almost 800 recent high-school graduates are preparing to take Verto classes in Costa Rica, Hawaii, England, Spain and Italy in the fall.

Temple University liked the idea of students who already had a leg up in college coursework, said Vice Provost for Admissions Shawn Abbott. The university is expected to receive about 12 students this fall who studied abroad with Verto in the spring. Because Temple doesn’t offer the program exclusively to its wait-listed students, Verto students who are interested in enrolling in the college apply as transfers.

“We communicated to them that rather than waiting for us to make a decision as to whether or not we can offer a space for the fall, here is a direct conduit into Temple,” said Mr. Abbott, referring to wait-listed students.

Write to Aydali Campa at aydali.campalopez@wsj.com