Photo: Caps flying during the 2015 graduation at Belmont High School.

“Bittersweet,” is how Lisa Castagno would feel watching her daughter, Olivia, receive her diploma along with 274 of her classmates during graduation ceremony for the Class of 2015 at Belmont High School on Sunday afternoon, June 7.

“I’m really happy but sad,” said Castagno, who has seen three daughters graduate from the school, with a son remaining. “It’s great to see them growing up. It’s an exciting time for them and for us parents but in a different way.”

Amidst cheers, hugs, contemplation, photos and a cloud of cigar smoke, 275 seniors transformed from students to alumni during the ceremony held in the school’s Wenner Field House.

“Your child charmed us, and at times alarmed us, they have pushed the boundaries of learning and thinking to new horizons,” Belmont High Principal Dan Richards told the graduates and those who packed the Field House.

“We will miss their energy and their endless ideas, but know that each of them will put that creativity and intelligence to good use,” he said.

Class President Sophie Kunz-Cosgrove said this graduating class “cultivated a culture of hard work, determination, and caring, in and out of the classroom.”

“After today, we will start our lives apart. But we built something here that will always be with us; a community, our community where everyone is different but everyone belongs,” she said.

Thomas Zembowicz, the first of the speakers honored with the School Committee Award for Outstanding Achievement in Scholarship – whose long list of accomplishments in academics, volunteering and athletics read by School Superintendent John Phelan seemed to embarrass him slightly – said what he will miss the most from his experience at Belmont High is “a feeling of contentment and belonging … in even the most mundane situations” hearing snippets of conversations or watching classmates working together on projects.

“I reflected on the rituals that bind us as a class; unscripted and unnoticed … noticing these shared routines … gave me a more powerful sense of nostalgia,” said Zembowicz, who will matriculate at Yale in the fall.

“Take a minute to notice the forged ties with people that shared things with you, even if that means just sharing a table at the library,” he said. “Because even as the past weeks events slip out of our memories, we will always have each other.”

Organization, for Catherine Tang, the second School Committee Award speaker, was the touchstone of her experience at Belmont High School. How she studied and practice, Tang did each within a tidy planned “comfortable” system. That was until the day her art teacher, Mark Milowsky, squirted a tube of paint on her blank canvas.

“Mr. Milowsky said, ‘You need to learn to trust yourself’,” Tang said. Despite being out of her comfort zone, she created a work that she remains most proud.

“We all have our plans, our systems, our expectations for the future. But we may find that someone splatters paint on our canvas,” said Tang, who will not travel far to attend Harvard College this fall.

“It is up to us to decide what we make of the unexpected situations that life throws at us, whether we view them as obstacles or as opportunities for personal growth,” she said.

“Don’t worry about the unexpected; trust your abilities and put your mark on the new and unexpected.”

Finally, it was time for the 275 students to become former pupils, to shake hands with school committee members, superintendent, and principal; then tossing caps in the air, and meet outside for photos and cheap cigars.