WALTHAM — The young Celtics star Jaylen Brown was locked in a fierce one-on-one battle.

Standing on the leprechaun logo at center court of his team’s practice facility, Brown was a good foot-and-a-half taller than his opponent. Still, the crowd that surrounded the two adversaries unanimously favored her.

“Gi-a-na! Gi-a-na!’’ they chanted, loudly. Giana Prieto, 13, pounded her right fist into her left palm three times, facing off against her rival in the afternoon’s final round of Rock Paper Scissors.

Giana was one of 30 students from her middle school, the Wetherbee School in Lawrence, and 30 more from neighboring North Andover Middle School, who were on hand at Celtics’ practice on Martin Luther King Jr. Day, Jan. 15. It was the culmination of a series of workshops the Celtics have conducted with students from the two schools, an innovative outreach program designed to engage students in dialogue about diversity and inclusion, and what they can do to encourage them.

Over the course of several workshops beginning in October, the students and members of the Celtics organization designed a “playbook’’ — a handbook featuring various troublesome scenarios the kids themselves came up with, and the ways they might intervene. The scenarios include fictional incidents of casual racism and bullying, gender bias, and insensitivity to religion, disability, and orientation.

Conceived in partnership with Play Ball! and the Celtics’s Shamrock Foundation, the playbook initiative has caught the NBA’s attention as a model of next-step commitment for the league’s community outreach programs. At the Celtics’s practice facility, Play Ball! founder Mike Harney credited Celtics coach Brad Stevens and his wife, Tracy, with the idea of engaging two neighboring schools.

“He never takes credit,’’ said Harney of Stevens, “but this was his brainchild.’’

“It’s wonderful for the two communities to connect around something so important to both of us,’’ said Jennifer Price, superintendent of schools in North Andover. “We’re crossing the bridge, literally.’’

After the students, all dressed in green T-shirts, watched the Celtics practice, they sat down for pizza in the team’s conference room. Stevens thanked them for participating in the program, noting that this year’s Celtics roster features players from all over the globe, including Australia, Germany, France, and Egypt.

Quizzing the students on which current Celtic was born in Australia, he joked that even his own players have gotten it wrong. (It’s Kyrie Irving. Aron Baynes, who is Australian, was born in New Zealand.)

“Obviously, we’re as diverse a group as you can get,’’ said Stevens. “It’s pretty special to be a part of that.’’

After an icebreaker, Brown, Baynes, teammate Semi Ojeleye and assistant coach Jerome Allen sat down courtside facing the students. Dave Hoffman, the Celtics’s senior director of community engagement, had them read one of the scenarios. In it, a group of kids make a YouTube video full of stereotypes.

In their own youth, Hoffman asked the Celtics, how would they have handled such a situation?

Baynes, wearing corduroy slippers and an enormous pair of sweatshorts, joked that he probably would have suggested the kids make a reckless stunt video instead. Brown was a little more reflective.

“I would have probably flipped the script,’’ he said. “I would have made the little kid the bully and the big kid the nerd.’’

Celtics co-owner Steve Pagliuca stood on the sideline grinning. Brown, he noted, was a chess champion in high school.

His ownership group had three main objectives when they purchased the franchise in 2003, he said: to win a championship, improve the fan experience, and create a world-class community outreach program.

“We try to impact the lives of kids,’’ he said. “This really ties into what we’re trying to do.’’

The students each took home a copy of the finished playbook, printed on heavy stock and designed to look like a coach’s clipboard. Next, they will meet with elementary school students to pass along the insights they’ve learned.

Timmy Briley, a 13-year-old from North Andover wearing a Tyler Zeller jersey, told the group he appreciated hearing some of the players’ own stories — “guys in the locker room saying stuff that they shouldn’t.’’

As the students gathered their coats and headed for the buses, Hoffman reflected on the success of the program.

“It verified how sorely needed this is right now,’’ he said.

James Sullivan can be reached at jamesgsullivan@gmail.com. Follow him on Twitter @sullivanjames.