The U.S. National Science Foundation (NSF) has halted a program that each year allows hundreds of the nation’s best graduate students to work with experts in another country. And the agency isn’t saying why—or whether the program will resume.

Begun in 2013, Graduate Research Opportunities Worldwide (GROW) is a perk of NSF’s flagship Graduate Research Fellowship (GRF) program. Students already receiving the $34,000-a-year fellowship can apply for an additional $5000 GROW allowance to cover travel and living expenses incurred while working in one of 17 countries. NSF has budgeted for up to 400 GROW awards a year (2000 GRFs are chosen annually) for foreign collaborations lasting from 3 to 12 months.

Students typically apply in the fall. But this year, those who tried to submit a proposal were informed that NSF’s online system, called FastLane, would not accept them.

That news was a huge disappointment to Claire Fox, who had hoped to explore the early evolution of flatfishes at a marine research facility in India. “I was counting on this funding to support the last chapter of my dissertation,” says Fox, a Ph.D. student studying under William Bemis, an evolutionary biologist at Cornell University. Fox had also arranged to work with Indian colleagues on a project to improve precollege science education.

The rejection of new proposals was a big surprise to Jan Allen, an associate dean of the graduate school at Cornell, home to more than 200 graduate research fellows. She had just put on a workshop in which previous GROW recipients offered tips on how to apply for the award.

The idea of working abroad was beginning to gain traction among the fellows, Allen says. “It gives students a global research perspective, something that’s increasingly important in today’s world.”

NSF declined repeated requests from Science Insider to discuss the status of GROW. The agency’s most recent GROW announcement was posted in fall of 2017; it refers to an October 2015 Dear Colleague letter that gives details on how to apply. In past years the deadline has been set in early December, with awards made the following spring.

Seventeen countries have inked bilateral agreements with NSF to participate in the program, and applicants are vetted at both ends. The host institution can also provide students with an additional monthly allowance to cover living expenses.

Calen Henderson was part of the inaugural GROW class in 2013. A graduate student in astronomy at The Ohio State University in Columbus at the time, Henderson spent 3.5 months at Chungbuk National University in Cheongju, South Korea, learning how to apply gravitational microlensing to hunt for exoplanets. Now a research scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, he can’t say enough about how GROW has enriched his scientific perspective.

“My adviser [Scott Gaudi] always said Ohio State had everything a student needed to complete their degree and that there had to be a compelling reason to go elsewhere,” Henderson explains. “Well, [Cheongbuk astronomy professor] Cheongho Han is the world’s expert on gravitational microlensing.”

The GROW awards require students to weigh the benefits of studying abroad against the loss of productivity at home. Gaudi had already collaborated with Han in developing the technique but was still concerned about how long his student would be out of the country. Henderson had a ready answer.

“I said I could probably learn the basics in a week or two,” Henderson said, “but that after 3 months I could get really good at it, and maybe even find new ways to apply it.” The collaboration also led to a joint paper with Han that Henderson says helped him appreciate the differences between the two scientific cultures.

“We write down the same equations,” Henderson says. “But we use different paradigms to solving problems. And learning about those differences is really valuable in building a relationship.”

The opportunity to learn about a new culture was a driving force for Debra Hausladen in applying for a GROW award. “I have always liked having an international component to my research,” says Hausladen, who spent 3 months at the University of Shizuoka in Japan starting in late 2013 learning new techniques for understanding soil carbon cycling as part of her work with biogeochemist Scott Fendorf at Stanford University in Palo Alto, California.

Hausladen has maintained her globetrotting ways after graduation. She’s now finishing up a postdoctoral fellowship at the University of Lausanne in Switzerland and has accepted a tenure-track position in the civil and environmental engineering department at the University of Sherbrooke in Canada. “They were impressed with my international network,” she says.

Only a tiny percentage of GRF recipients apply for a GROW supplement. Allen says Cornell graduate students have received 11 GROW awards since 2014, but she thinks that number will rise as more students and faculty members become aware of the opportunity.

For GROW to grow, however, NSF must once again let eligible graduate students apply for an award. Officials aren’t saying if, or when, that will occur.