WARMINSTER, Pa. (AP) — Those attending a suburban Philadelphia high school commencement ceremony this month will see a lot of familiar faces: The school plans to graduate no fewer than 14 pairs of twins.

The 2014 graduating class of William Tennent High School in Bucks County includes five sets of male twins, seven sets of male/female twins and two sets of female twins.

School principal Dennis Best said he isn’t surprised by the number among the 485 graduates.

“I am reminded of this on a daily basis while walking through the hallways and wondering ”˜How did I just walk by the same student twice?”’ he said.

The twin birth rate rose 76 percent from 1980 through 2009, from 18.9 to 33.3 per 1,000 births, the U.S. Centers for Disease Control and Prevention reports. That means one in every 30 babies born in the United States was a twin in 2009 compared with one in every 53 in 1980.

Researchers have attributed the increase to growing use of fertility drugs and treatments and more births to older women, since mothers in their 30s are more likely to have twins than younger or older women.

One student, Nicole Alden, said being a twin with her brother Matt brings social advantages as her sibling has friends the same age, calling it “the best of both worlds.”

“There’s always knowing someone is there for you because they’ve been with you your entire life,” Matt added.

Nicole Teeter, a biology teacher at Tennent, praised the sets of twins as being “some of the best kids in the school.” “They’re a really nice group,” he said. “They’re polite, they’re active, they’re involved in the community and the school.”