The school is sending its top boys' and girls' teams to the under-16 Flag Nationals in southern Ontario later this week, and both squads have an eye on a championship.
Uptake in the sport has exploded in recent years at SIS, with physical education teacher John Turner creating a competitive club program.
"John Turner's created a monster here," said Trevor Bridges, who will coach the boys' team at the national tournament.
"We have so many flag football teams going that... when they get to the grade 8 and 9 teams, they have a lot of the basics down already.
"We're feeding into the program really good. Other schools haven't caught up to us yet."
Some six other Island schools also compete in flag football at the provincial level, but the depth of the SIS program has led them to victory in the past three PEISAA championships.
As such, the winners of the SIS club championship tournament earned the right to play at the nationals.
Until recently, teams competing at the nationals were required to be co-ed, with at least two girls on the field during games. Now the boys and girls have been split into separate divisions, something that points to flag football's growth across the country and on the Island.
"The girls have a lot of fun with it," said Turner, who will coach the SIS girls' team in Ontario. "They can compete at the national level along with the other big provinces like Quebec and Ontario. It shows that a little place Summerside, P.E.I., can develop players if they're in a good program for two or three years."
Both of the local teams hope their experience at the nationals will play a role at this year's tournament.
Brohan Brennan has quarterbacked the boys' side for the past three years and is ready for another shot at gold.
"A lot of our guys are older, they're returning guys, so I think we have a better chance this year of winning a few games at least and, if we're lucky, getting pretty far (in the tournament)," he said.
Experience can mean a lot in flag football since, unlike the tackle version of the sport, size is not always the biggest factor.
The boys' speed made them a good matchup with other teams at last year's nationals, like some British Columbia players who stood over six feet tall.
"In flag, especially for the girls, it's about speed," said Turner. "(Defensively), grabbing the flag is the key. You can't give up the extra yards, so if you're there to make the tackle, you have to make it, otherwise it's an extra four of five yards and you just can't do it."
Turner's girls' team includes four players returning from the defending silver-medal team, which hopes to avenge a loss to Quebec in last year's gold-medal final.
"Mr. Turner always tells us to execute our plays, and we practice them a lot, so I think we'll have a good shot at doing that," said returning team member Carrie McGuire.
Similarly, Bridges said the boys will have to complete passes in order to take advantage of their speed.
"If the boys can execute their offense, we'll be OK," he said. "If they're dropping the ball, we're in trouble. It's as simple as that."
The teams leave for Ontario this Friday, with both teams playing their first round-robin games at 11 a.m. on Saturday. The boys take on Quebec, while the girls face Manitoba.
For the full schedule and results, visit: footballcanada.com.