The pregnant actress brought fiancé Jason Sudeikis along with her to Phillips Academy in Andover, Mass., where she formerly attended high school.
Bundled up in winter gear, the duo gave several students quite the surprise on Friday as they ventured around the campus of the historic school, which is located just over 20 miles north of Boston.
The pair posed for pictures with several students, and even spent some time in the photography classroom helping people develop photos.
"While I was working, I heard the door open and there was Olivia and then Jason!" Lily Zildjian, a senior at Andover who was working in the photo room when the celeb couple walked in the door, tells PEOPLE, adding that word spread fast that the pair was on campus.
Sudeikis toted his own camera while the couple hung out, and both he and Wilde took the time to ask Zildjian about the pictures she was working on and the process of developing photos.
"They even helped me and told me which negatives they liked the best,” Zildjian says.
Sudeikis also chatted about his love of playing the drums after noticing Zildjian's last name, which is one of the biggest cymbal companies in the world (her father is president of Sabian Cymbals).
Meanwhile, Wilde reminisced about her time living on campus during her years at Andover.
"They were such nice people," said Zildjian. "It was completely unexpected to meet them and such a cool experience to just talk with them!"
Sudeikis is currently in Massachusetts to film the movie Tumbledown with Rebecca Hall and Joe Manganiello. They were spotted enjoying a coffee date just a few days prior near filming.