SOUTH BEND, Ind. — Eric Cavaliere has been watching Ian Book play football for over a decade, stretching back to when Book was 9 and Cavaliere was in attendance only because his daughter was a cheerleader.

Cavaliere says he has seen almost every game Book's played since, be it live or on TV.

For all the prolific numbers Book posted while going on to star at quarterback for Cavaliere at Oak Ridge High School in El Dorado Hills, California, and for all that Book has already achieved over his first three outings this season as the full-time starter at Notre Dame, it's a moment on the sideline during Book's sophomore season that sticks out to his former coach.

"We're late in the heat of this playoff game, this great comeback from 21 down at halftime, a game Ian took over," Cavaliere recalled of a 45-42 overtime victory against Jesuit in 2013.

"Ian spots our athletic director, Steve White, who's also his math teacher, and starts asking about the math test he took the day before, starts wondering how he did," Cavaliere said of Book, an A-minus student. "Ian says something like, 'Boy, question 14, that was a tough one,' and his teacher is like, 'Hey, focus on the game.'

"But that's the thing about Ian," Cavaliere said. "He had things under control. He's cool and calm and is not going to let anything emotional overtake him. He can handle situations."

While it remains a small sample size, Book has displayed similar traits for the fifth-ranked Fighting Irish (6-0), who host Pittsburgh (3-3) on Saturday.

Lightly recruited compared to the players Notre Dame typically lands, Book isn't big by college quarterback standards, just 6-foot, 203 pounds. Nor is he fast or flashy.

He's just effective, and the junior's been working to be just that since he arrived in South Bend..

"I've been trying to prepare like I'm the starter since I've gotten here," Book said after steering the Irish to a 45-23 road win last week at Virginia Tech.

"(I've thought) when it's my time, it will make it that much better," Book said. "It would really suck to not be ready if your name was called. It's just something I focused on since the day I stepped on campus as a freshman."

Book did not play as a freshman. As a sophomore, he started one game, at North Carolina because Brandon Wimbush was out due to injury, and helped the Irish win 33-10. In the Citrus Bowl, he came off the bench to rally Notre Dame to a 21-17 victory over LSU.

Wimbush, a senior, initially took the starting job back this season, but now Book appears entrenched.

In the opening three games with Wimbush — all at home and just one against a ranked opponent — the Irish averaged 23.3 points and 365 yards of offense. In Book's three starts — two of them on the road and two against ranked opponents — Notre Dame has averaged 46.3 points and 518 yards of offense.

Overall, Book has completed 77 of 105 passes for 887 yards with nine touchdowns and one interception. He's third in the nation in completion percentage (73.3). Wimbush is 42 of 76 (55.3 percent) for 589 yards, one TD and four picks.

While Wimbush remains the more explosive runner, Book has demonstrated a knack for gaining key yardage with his feet, and he's drawn praise from coach Brian Kelly for being able to sense the rush, extend plays and throw accurate passes on the move.

Kelly first became fully aware of Book after naming Mike Sanford his offensive coordinator in March 2015. Sanford, who has since become head coach at Western Kentucky, became interested in Book in 2014, while he was coordinator at Boise State. Book verbally committed in April 2015 to Washington State after Sanford left, but the coach renewed his pursuit of the three-star prospect after joining the Irish.

"I remember when Notre Dame wanted Ian to visit, he said, 'Coach, I just don't want to be a flipper,'" Cavaliere recalled of Book's commitment to Washington State, "but I said, 'Ian, this isn't just another school, this is Notre Dame. You have to at least look at this.'"

Book and his family added a South Bend stop to an already planned summer vacation. He committed soon after in August 2015.

"There were a lot of things that attracted me here," Book said. "I wanted to get a good education, the tradition. I came on campus, and like a lot of people say, once you step foot on campus, it's just that feeling you get."

Wimbush was already aboard as the nation's No. 2-ranked dual-threat QB in the 2015 class by Rivals, and the Irish were also seen as contenders for a top-rated QB in the 2017 class. Book was not in that discussion, yet here he is.

"Wherever you go, there's always going to be a quarterback in every class," Book said. "I knew who Brandon was, I know he's a good player, (but) it wasn't something I really tried to focus on, because every class is going to bring in a good quarterback. There was an open spot here."

Book's commitment was widely second-guessed on social media. Cavaliere, who is in his 12th season at Oak Ridge, said recruiting is a funny thing.

"We've had a lot of athletes an inch short or a 10th (of a second) slow, compared to the four and five-star kids, but Ian's one of them who's always been able to play football," he said. "Those demographics of height, weight, speed are sometimes too important as opposed to what they can do on a field with teammates. Ian's an example of that. He makes smart decisions and gives his teammates opportunities to make plays."