Gonzaga, pictured at Monday’s WCAC lacrosse final, has long been the standard for D.C. high school lacrosse, but the game is gaining traction at public schools in the District. (Toni L. Sandys/The Washington Post)

The first time Mike Collins led a practice with what would become his School Without Walls lacrosse team, he instructed four interested students by using three of his own sticks to run through drills with one ball. He told them to bring friends next time — if they’d had fun. The next week, eight players showed up. Soon, there were 15. Then, more than 20.

As his team played through a patchwork schedule in 2013, Collins discovered several non-traditional lacrosse schools also hoping to turn growing interest into well-organized varsity teams. So before this season, he established the Washington Interscholastic Lacrosse League.

KIPP DC, the Lab School, St. Anselm’s Abbey, Wilson and School Without Walls played home-and-home series this season, vying for four slots in the league’s inaugural postseason. Wilson and St. Anselm’s emerged from Monday’s semifinals — the first playoff lacrosse games to include D.C. public school teams — and will meet in the WILL championship game Friday at Wilson.

The league is not funded by D.C. Public Schools or any other organization, so “it’s all grassroots volunteers,” Collins said, adding that “there are a lot of people doing this by force of will.”

Wilson is the most established team in the group and the biggest school in the league, and its athletic department opted to sponsor the team as if it were a regular DCPS varsity sport. Collins funded last year’s Walls team out of his own pocket and with his own equipment before receiving a grant from U.S. Lacrosse this season. KIPP funds its own team, while Major League Lacrosse and National Lacrosse League star Paul Rabil sponsors the new team at the Lab School. St. Anselm’s Coach Mark Kent, who is a co-founder of Bethesda club program Next Level Lacrosse, funded his team for two years before the school decided to sponsor the team.

WILL coaches made the investment after seeing that from St. Anselm’s — a school of 248 boys from grades 6 through 12 — to much larger Wilson, interest in the game was percolating among D.C.’s non-lacrosse schools.

Wilson senior Andrew Arlotto, who has played for the Tigers since his freshman year, says he has seen a notable difference in the teams at Walls, Lab, KIPP, and St. Anselm’s in a short time.

“Now in my senior year I’m seeing all these teams come up,” said Arlotto, who will play at Division III Bard College (N.Y.). “We just played KIPP, and the amount of energy and passion these kids have for a sport that’s not really as developed in D.C. as basketball and football is really something special.”

Wilson, which has had a team for five years, is undefeated against WILL foes this season. Despite not having been in a league in previous seasons, the Tigers have been able to schedule D.C. private schools such as Sidwell Friends and Maret. That competition helped grow the team, something Coach George Arlotto hopes can continue through WILL.

“It’s really hard for a Wilson or a Walls to go out and play against a St. Albans or Gonzaga because those are really good teams,” Coach Arlotto said.

Learning the game, rather than jockeying to play it at the next level, is the purpose of WILL, “a developmental league,” according to Kent, whose Next Level club players go on to Division I programs after careers at top high school programs such as Georgetown Prep, Gonzaga and Landon.

“We understand that we aren’t on the same status as a lot of those private schools with lacrosse yet, but we feel we’re becoming better, improving ourselves,” said Walls sophomore Matthew McAllister, who began playing as a freshman. “Our coach always talks about being a part of something new, and it feels great to be a part of one of the first lacrosse teams and play in the first playoff game for D.C. public high schools.”

The league and those playoffs added meaning to seasons Arlotto said used to be played only for “respect,” and they gave incentive for new teams to stick together and commit fully.

“The fact that we did have playoffs shows the sport is progressing,” Walls senior Curtis Williams said. “It’s getting more and more popular, and I hope DCPS can recognize it as a varsity sport soon.”