CAMBRIDGE -- It had been two days since the college students had taken a shower, and they were filthy.
Covered in dirt and grime from cleaning up a Pennsylvania state park, they eagerly anticipated hot showers at a Cambridge homeless shelter, which they cleaned top to bottom yesterday before boarding a bus to help poor families in New York City.
A whirlwind cross-country volunteering tour is not a typical way to spend spring break, but it is how these 38 University of Minnesota students choose to illustrate the ''Pay It Forward" concept popularized by the 2000 movie in which one good deed led to another.
For one week, instead of tanning on an Acapulco beach in Mexico, the students are picking up trash, scrubbing graffiti, and trying to spread hope -- one act of kindness at a time.
''If we go and show that people are willing to travel around and do something for others, then it shows that it can be done on a much smaller scale," said Laura Carter, 20, a marketing major from the Minneapolis-St. Paul area. ''We go on these trips to help others, but really, in the end we help ourselves."
The students boarded a charter bus in Minneapolis at 10 a.m. Friday. Ten hours later, they arrived in South Bend, Ind., to volunteer at a food bank. From there they took the bus to Lancaster, Ohio, to clean graffiti and paint an old covered bridge. Sunday, they arrived in State College, Pa., and the next day they spruced up trails at Black Moshannon State Park.
Monday, they arrived in Cambridge, where they slept in classrooms at University Lutheran Church near Harvard Square. Some of them rode the T for the first time, and during a rare bit of free time, visited the Boston bar made famous by the TV show ''Cheers."
Yesterday, they rose early and cleaned the Harvard Square Homeless Shelter in the church basement, mopping, dusting, and folding clothes.
''I was interested in doing something for other people," said Sarah Simpson, 19, a freshman chemistry major from Rolla, N.D. ''I would have just gone home and done nothing all week if I hadn't come here. I've never been to Boston or New York before, and this is pretty neat."
The students left Boston yesterday afternoon and went to New York, where they planned to help restore apartments for low-income families. Then they go to Washington, D.C., for a joint conference with the seven busloads of about 320 Midwestern students whose pay-it-forward experiences took them on different routes across the country.
In Washington, the students are scheduled to meet Catherine Ryan Hyde, whose book inspired the movie. They also hope to complete one collective project: helping to tidy the Anacostia River area. They have to return to class in Minneapolis by Monday.
Their pay-it-forward college movement was founded by four University of Minnesota students, who started a small tour in 2004 and expanded their organization to several Midwestern colleges and universities. It takes six months to plan each route, according to the group's website. The students raise money and are asked to pay a $425 registration fee to help cover the cost of the charter bus.
The Cambridge homeless shelter was also a stop of one tour route last year, said Corey Kranz, 21, one of the student leaders.
''Back in Minnesota, we unrolled a map, and someone said 'I really want to go to Boston, so let's do it,' " said Kranz. ''This is a revisit."
In Cambridge, after taking their long awaited showers, the students completed the sort of work that regular volunteers can't do every week, said church leaders.
''This was a deep clean," said church administrator Jayms Battaglia. ''This was needed."
They also spoke with Harvard students who also volunteer, and run, the homeless shelter. After the cleanup, church elders made chili, which the students wolfed down before grabbing their sleeping bags and walking two blocks to where their bus was parked.
Many of the students tried to catch a glimpse of the Harvard campus before boarding their bus.
''It's a way for you to step out of your comfort zone and to pay it forward to ourselves and to others," said Rebecca Agnitsch, 20, of Baldwin, Iowa, who raved about Boston's rainy yet warm weather as compared with snow-covered Minnesota. ''We may not see it or know it, but I think that this has a big effect on people."
The students have a guest -- a University of Tokyo political science major who is visiting an exchange student at the University of Minnesota. Yoruzu Kenjiro, 20, said he tagged along because it was a good way to see ''the real America" and hang out with US students. Kenjiro said he had to get used to loud and rambunctious behavior, some of which could be considered rude in Japan.
''The best thing is that we can communicate with people in the community and in organizations like the church," said Kenjiro. ''I got a very precious experience."
Adrienne P. Samuels can be reached at firstname.lastname@example.org.