One part of Purdue's strategy is having students agree to follow the Protect Purdue Pledge, in which they promise to diligently wash their hands, don a face covering and practice social distancing.

But a different story was playing out down the street from campus.

As local media reports detailed in May, when Purdue hotspot Harry's Chocolate Shop reopened its business, students lined up in the pre-dawn hours to get a seat, bunched together nearer than the advised six feet and often maskless. This trend prompted unease among local health officials.

Similar tales have cropped up across the U.S. as many states battle a rise in confirmed coronavirus cases. Outbreaks have been tied to fraternity homes and bars, and the issue of mask-wearing has become deeply politicized.

So far, nearly a quarter of colleges plan to be mostly or fully in-person this fall and 16% are adopting a hybrid model, according to data from the College Crisis Initiative at Davidson College. A quarter of the some 3,000 institutions in the sample are still deciding. Only around 5% said they were going fully online, and even then they likely will offer some students housing on campus.

Behavioral experts say it's doubtful every student will abide by safety measures designed to prevent the spread of the virus to the extent colleges demand. While relatively few students are likely to deliberately flout the rules, others may make mistakes that void them unintentionally. And early indications of student behavior bode poorly for the coming year. That could undermine the linchpins of colleges' safety plans this fall.

Students share some blame when they don't follow the rules. But it's not all their fault. Campus leaders should acknowledge that college students' brains are still evolving in a way that makes them prone to taking risks that could endanger them — especially considering they've likely been pent up for months. Officials should also prepare to educate students and offer rationale for what they're asking them to do, all in an effort to normalize some of the required behavior changes.

"If you are asking people to change the way they socialize and hook up, then being able to explain why you need to do it differently I think is important," said Dominic Packer, a psychology professor at Lehigh University. "If people understand the reasons, then they can take that into account and it doesn't just feel like, 'Oh we're being told what to do because they don't want us to have any fun anymore.'"

The pull of social connection is particularly strong among students in the traditional college age range, said Anna Song, a health psychology professor at the University of California, Merced, who studies risk-taking and adolescent behavior.

A global health crisis hasn't curtailed their fun. The examples are numerous: A rash of cases in June was linked to a bar frequented by Louisiana State University students. A pub popular among students at Michigan State University was found to be the hotspot for at least 170 cases, contributing to the governor's decision to stop indoor service among establishments that primarily serve alcohol, according to The Associated Press.

Colleges are setting campus policies that may prove difficult to enforce in part because students aren't likely to follow them, whether on purpose or through oversight. Harvard, Virginia Commonwealth and Seattle universities, as well as the University of California, Davis, are among the schools to ban visitors in on-campus housing, as one example.

"There are a lot of things working against helping young people socially distance and be vigilant against COVID-19," Song said.

Of the seven, four-year nonprofit institutions Education Dive contacted to discuss their rules and expectations for student behavior this fall, only one provided comment by publication time: Purdue.

Mistakes and "oversights" will likely occur among students, and issues with compliance will be addressed with "care, understanding and information sharing," spokesperson Jim Bush wrote in an email. Purdue plans to offer a mix of online and in-person classes this fall.

"We understand that these changes are significant in a person's day-to-day activity, and it may take time for new norms to be fully implemented," Bush said.

Colleges will try to give students some leeway, especially early in the year, said Martha Compton, president of the Association for Student Conduct Administration and dean of students at Concordia University Texas. Students won't be removed from campus if they forget to wear a mask to class or stop to talk with a friend, she said. Administrators will try to educate, rather than be punitive.

But officials will find ways to come down on students who blatantly disregard pandemic-related policies. Most conduct codes contain provisions that allow them to punish students for breaking miscellaneous campus rules or outside regulations and laws, Compton said.

While some students will ignore mandates entirely and throw gigantic parties, the misteps generally won't be massive or intentional, Song predicts. It's more likely the virus would be spread by students not thinking through their daily interactions. The brain doesn't stop developing until around age 25, Song said. Because of this, young adults generally have good intentions but may not think through their actions completely.

Song gave a scenario: A student walking down the street spots a friend they haven't seen for awhile. The two stop, hug and remove their masks to talk.

"It's a situation where the impulse completely outweighs the intention," Song said.

Not to say larger incidents won't occur. Outbreaks of the coronavirus have already been tied to Greek life parties at several institutions.

But the likely offenders will be one or two students who decide to host a party in an off-campus apartment, said Gentry McCreary, CEO and managing partner of Dyad Strategies, which consults with colleges about student life.

That could make punishments more difficult, McCreary said. Colleges will need to rely on partnerships with local police and health departments to crack down on off-campus misbehavior, he said.

"College students are a sociable bunch, they're going to spend time together, it's part of the college experience and it's going to happen," McCreary said.

There's socializing, and then there's sex. Calling on students to forgo that kind of intimacy is "a really big ask," said Lisa Wade, a visiting scholar at Tulane University and author of "American Hookup: The New Culture of Sex on Campus."

Hookups are sexual encounters with no expectation of commitment. While research shows most students don't hook up all that much, the expectation is still there, particularly at residential colleges. So is the opportunity.

"The moments on college campuses where hookup culture is at its greatest strength are these massive parties where many, many students are mashed together and drinking alcohol and having a lot of physical contact of all kinds," Wade said.

But as college and government officials lay on rules to prevent the virus's spread — such as banning guests in campus housing and limiting how many people can gather — they're also narrowing the pool of people who students can readily interact with, and the venues that kindle hookups.

That doesn't mean students won't try, said Justin Garcia, executive director of the Kinsey Institute at Indiana University, which studies sexuality, relationships and well-being. He questioned whether students will turn more to dating apps as an alternative for finding sexual partners.

If college officials can be honest that students will seek out sex amid the pandemic, Garcia said, they "can be a lot more effective at providing students with tools to stay safe and to reduce risk for both themselves and everyone else in the community." He added that the health crisis gives colleges a chance to offer inclusive sex education that covers disease transmission.

Students can take precautions such as getting tested for the coronavirus and quarantining between sexual partners, as well as being open with roommates if they're hooking up, Garcia said.

Colleges "need to actively start the conversation" with students "about how to reimagine their sexual and romantic lives" in light of the pandemic, Wade said, noting that some students may not know how to date or have preconceived notions of how to have fun on campus. Schools also haven't delved too deep into discussions of campus sexual culture, focusing instead on helping ensure students have safe sex and reducing sexual violence, she added.

One way colleges can guide students now is by setting up discussions across campus between students who live in dorms and their resident advisers, Wade said. Colleges could also give students more opportunities to socialize in environments designed to prevent the virus from spreading.

But telling students to abstain? "That's not realistic," Garcia said. "We could tell them that, but that's not realistic for anything that we know about the last century of behavioral science. Let's arm them with realistic tools."

Colleges bringing students back to campus are also banking on their willingness to wear face coverings — and doing it right. But Syon Bhanot, a behavioral and public economist who teaches at Swarthmore College, doesn't think that's a sure bet.

"There's a great deal of uncertainty about how seriously students will take these procedures," Bhanot said.

Research has shown that masks are effective in reducing the virus's spread. And behavioral science suggests some degree of mask-wearing can be expected in public spaces like classrooms, where peoples' actions can be observed and sanctions can be readily administered. But it's "extremely uncertain" whether it will be the norm in more private settings, Bhanot said. Think dorms and off-campus apartments.

If masks are to become ubiquitous for students, colleges have to set that expectation, behavioral experts said. But in a country where mask-wearing is still a relatively novel behavior, colleges must do more than ask.

A key part of social norms is understanding how other people expect you to behave. Colleges' messaging to students should reflect that, Bhanot said: "Everyone's expecting you to wear a mask here on campus and you are being judged negatively if you don't."

For the message to stick, students need to hear it from other students, particularly those in leadership positions, said Catherine Sanderson, a psychology professor at Amherst College and author of the book "Why We Act: Turning Bystanders into Moral Rebels," which examines the psychology of changing social norms.

"Getting some people in an environment to adopt a particular behavior creates a ripple effect and leads other people to follow," Sanderson said. "You don't change everybody, you just change the right people and then other people will follow."

The intervention applies to more than just mask-wearing.

West Virginia University, which is starting the fall with a mix of online and in-person classes, has tapped around 400 students and 200 faculty and staff to help turn their classmates and colleagues onto the requirement. These "micro-influencers" hope to encourage people "who have not yet decided how seriously they'll take our campus safety guidelines" to wear a mask and follow other coronavirus-related rules, Tony Dobies, a university spokesperson, wrote in an email.

The university sent each of them a school-themed mask and asked them to post photos on social media of themselves wearing it along with a reason why doing so is important. They even have a catchy name: Maskots.

That kind of approach can also help ensure students follow the rules when instructors and administrators aren't watching.

"It can't just be that (students) look around at each other and just sort of use each other as a guide, because there's definitely going to be students who don't wear masks," Bhanot said.

The guidance should also be to the point. "People respond well to concise, clear categorical asks: Do this, don't do this. This is good behavior, this is bad behavior," he said.

Another way to encourage mask-wearing is showing students how their actions affect others, Sanderson said. That could include reminding them that they are protecting a vulnerable worker, such as a favorite dining hall employee who is older and has a sick spouse at home.

Nationally, masks have been divisive. President Donald Trump largely eschewed them until late July. And while two-thirds of states require people to wear masks in public, some governors have come out against such mandates — a position that stands to impact colleges in their states. Meanwhile, businesses across the country say enforcement is a challenge.

Colleges may be welcoming students from areas with different norms around mask-wearing. To depoliticize the topic, Bhanot advises institutions to position themselves, rather than politicians, as the authority for safety rules on their campuses.

"The more the college can say, ... 'Those debates can rage on, but this is how we're doing it here and you have to adhere to that,' I think probably is going to be more effective," he said.