CIRCLEVILLE, Ohio (AP) -- Being a middle-school history teacher is difficult enough, but Rod Smith sees double in the classroom.
Smith teaches many of the eight sets of twins in the eighth grade at McDowell Exchange School in Circleville, about 25 miles south of Columbus. He has taught twins before over his 30-year career, but he said this group is different.
"They are more socially adjusted than some of the twins we've had here," he said. "Because there's just so many."
The eight sets include three identical pairs and two sets with a girl and a boy. All of them are 13 or 14 years old.
"Instead of calling us by our names, they say 'the twins,'" said Cheyenne Brannon, who looks a lot like her sister Chelsea even though the two are fraternal.
The mothers of three of the sets are friends, and their twins grew up together.
Evan Fouch is best friends with Luke and Lance Konkle, and twin Hallie Fouch calls Katherine and Caroline Waidelich two of her closest buddies.
"It's neat to see them all grow up together," said Gale Fouch, Evan and Hallie's mother.
Twins are becoming more common because of the use of fertility drugs. About one of every 33 babies born in the United States is a twin, according to the Centers for Disease Control and Prevention. Records show the number has increased more than 80 percent since 1980.
While acknowledging some of the school's sets arose from fertility treatments, the parents declined to say which ones.