In the early 2000s, after Mike Shanahan had won a pair of Super Bowls with John Elway and turned over play-calling duties to Gary Kubiak, the Broncos coach would lean on a trusted facet of practice to test his young coordinator’s mettle: The “call-it” period.

Shanahan would break out of the flow of a normal practice, telling Kubiak there’d be a segment of the session where he’d have to call plays on the fly, without the benefit of a coaching staff in his headset or a prearranged script of plays. Those periods prepared Kubiak for the flow of a game, and they were where he proved his mettle to his boss.

“I leaned on those periods a lot,” Kubiak said. “Mike made me do it a lot. When I was a head coach [in Houston and Denver], I made my guys do it a lot. Really, as a head coach, that’s how you find out about your coordinators, when you watch them call practice and watch them call situational football. You’re preparing them for game day just like you’re preparing a player.”

The incubation period Shanahan used for Kubiak then is the same that Mike Zimmer and Kubiak used this summer for Kevin Stefanski — their 37-year-old coordinator who’s got 13 years in the Vikings organization but still just three games of regular-season play-calling experience on his résumé. It was in those sections of practice where Stefanski could develop his feel for the offense and hone his nerve as a play-caller, before repairing to his office to review the day under Kubiak’s guidance.

“I walked up to him after we had that two-minute drill and I just said, ‘These situations are great,’ ” Zimmer said on Aug. 22. “He said, ‘They’re great for me because I don’t have anybody in my ear right now trying to help me, so I have to think of all this on my own.’ I think all those things help. On game day, obviously he gets help from other people, but it gives them an opportunity to practice being put in all these different situations.”

Stefanski is among 15 coaches beginning his first full season as his team’s offensive play-caller. Because of the deliberate preparative process he’s gone through with Kubiak this spring and summer, the Vikings hope he will be spared the rocky start that could come with his relative youth.

He welcomed the addition of Kubiak — winner of two Super Bowls as an offensive coordinator and one more as a head coach in Denver — as a wizened mentor, a year after John DeFilippo lost a close friend (and potential ambassador to Zimmer) following the death of offensive line coach Tony Sparano. Stefanski has encouraged collaboration across an offensive staff made up largely of Kubiak’s longtime assistants, and he’s made a regular habit of seeking out Kubiak’s perspective after those unscripted practice periods.

“He and I can sit there and have some really meaningful conversations, whether it’s coming off the practice field, or coming out of the meeting room,” Stefanski said this summer. “He’ll give me a couple pointers here and there, and it’s a resource I don’t take for granted. I think it’s incredible. He’s made me a better coach, just these last few months, because I enjoy being around smart people and passionate coaches and great teachers. Ultimately, that’s what we are, and I put him up there with the best of them.”

On game days, Kubiak will be in the coaches’ booth while Stefanski is on the field. Kubiak will chime in occasionally with suggestions for play calls, but much of his feedback will come between series, when the defense is on the field, and in the locker room at halftime. He knows as well as anyone there needs to be a clear chain of command on offense — with Stefanski at the top of it.

“You can’t be hemming and hawing on headsets with people,” Kubiak said. “You’ve got to have a voice, and Kevin’s the voice. We’ve got a certain way we’ve got things set up, of how we help him with situational football, but to be fast and have a good rhythm, you can’t be arguing about, ‘What should we do here?’ You’ve got to know what you’re doing before you show up on Sundays; if it’s fourth-and-2, this is our number one call. I think the preparation’s the biggest thing.”

That’s where the Vikings believe their system can help Stefanski flourish in a year where nearly half the NFL is banking on the success of new play-callers. In his years of experience with the team, and in the access he has to a distinguished mentor, Stefanski is unique among the newcomers.

The Vikings hope his results will be, too.

“The number one thing, just from my perspective, he knows this football team really well,” Kubiak said. “He’s been here a long time, and he’s coached a lot of positions. He knows Diggsy [Stefon Diggs], he knows Rudy [Kyle Rudolph]. He knows these players really well, and that’s extremely important. You’ve got to know their strengths, and what they do best. And to me, good coaches pull from all their coaches. He’s got a good staff, and he listens. Together as a group, we’ve got to do a good job for him as he calls game day.”