"It's just the routine every day of getting up and going to school," said Troup, of Honeyfield Road outside Williamsport.
When his older brother Bill went off to college two years ago, keeping to that routine became his responsibility because his parents were up and out of the house before he had to leave for school, Troup said.
Missing school means falling behind on work, which can hurt grades, said Troup, the son of Nancy and William J. Troup III.
Perfect attendance hasn't hurt Troup's academic performance. He is a member of the National Honor Society, is a Maryland Distinguished Scholar and was a Student Athlete of the Month.
Even sports injuries didn't keep him out of school or from practice for football or track.
Troup leads by example, said Eric Michael, who coached Troup for three of the four years he played football at Williamsport High.
"He was one of those guys who even though he was injured, he was still on the practice field helping out," Michael said.
As one of the team's captains, his leadership sets the tone for the rest of the team, Michael said.
If someone wants to view him as a role model, Troup said that would be fine with him.
"The key thing is I don't do drugs," said Troup, an Eagle Scout and assistant scout master for Boy Scout Troop 17 of Williamsport.
A good immune system and luck have had roles in Troup's attendance, but so has his penchant for physical fitness, he said.
He eats healthful foods, and runs and lifts weights for up to 2 1/2 hours a day, five days a week, Troup said.
"I enjoy exercising," Troup said.
The closest Troup came to missing a day of school was last fall when he got a speeding ticket and had to go to court, he said. He wrote to the judge, however, and was able to get his court date changed to a day when school was dismissed early.
Troup, who tutors math, works at Weis markets and is a veterinary assistant, said he rarely misses work.
He will attend Salisbury State University in the fall to study biology and the pre-veterinary program. He hopes to attend Virginia Tech's veterinary graduate program.
His attendance habits will be good for his career as a veterinarian, he said.
As a veterinarian, he will have to be available when a client calls in at 4 a.m. because the dog isn't breathing, Troup said.
"You can't always put yourself first," he said. "You have to put others first sometimes."