Thirty-five minutes into his commute, Warriors rookie Jordan Bell, riding in the middle seat of a black Chevrolet Suburban, looks up from his iPhone to find Fourth Street gridlocked.

“It’s just because of all these one-way streets,” Bell says, raising his voice to be heard over a chorus of car horns. “That’s what you get, I guess.”

It is 7:17 on a chilly night in early September, and Bell is running late for a 3½-mile race, the annual JP Morgan Corporate Challenge in San Francisco. As his SUV idles in traffic, only a couple of blocks from the starting line, more than 10,000 men and women in sneakers and athletic shorts are waiting in an AT&T Park parking lot to hear Bell give a pre-run pep talk.

That anyone would hire him for such an appearance still amazes Bell. For much of his childhood, he seemed more likely to drop out of high school than to play for the defending NBA champions.

Bell’s emotional outbursts and apathy toward class were so severe that he had to attend three middle schools. Long before Golden State paid the Bulls $3.5 million for his draft-night rights, Bell was kicked off Long Beach Poly High’s freshman football team and forced to attend a special program for students with behavioral problems.

Now, as he prepares for the start of his first NBA training camp Saturday, Bell recognizes what — or, more accurately, who — was the driving force behind his feel-good story. Unlike many of the former athletes he now knows working relatively menial jobs in Southern California, Bell benefited from the guidance of two mentors: his mother, Carolyn Gray, and his high school coach, Sharrief Metoyer.

“I just hope they feel like they got something out of their investment,” Bell says as his SUV finally pulls into parking lot A. “There’s no doubt in my mind that I wouldn’t be where I am today without them.”

Some of Bell’s favorite nights growing up were when his family went camping indoors.

To simulate a campfire, his mom lit candles in the living room of their Long Beach apartment. Gray moved two couches closer together and tossed a sheet over them for a makeshift tent. Before going to sleep, Bell — the youngest of Gray’s five children — used a flashlight to make shadow puppets on the wall.

It wasn’t until years later, when Bell couldn’t turn the light on in the bathroom one night, that he realized the reason behind indoor camping.

With so many mouths to feed, Gray’s hourly wage working at L.A. County’s Department of Public Social Services couldn’t cover all the bills some months. She skipped meals many days to keep the lights on. When that wasn’t enough, the electric company shut off the power.

“We’d make it into a fun little thing,” Gray said. “Nobody knew what Mom was going through, though.”

When Bell was 10 years old, Gray began taking night classes at Compton Community College. She later earned her bachelor’s degree in human services from Cal State Dominguez Hills and was promoted to a supervisor in DPSS’ welfare department.

The boost in income, however, didn’t make reining in Bell any easier. His father had enlisted in the military and come back addicted to drugs. Though Gray said Bell’s dad still tried to stay involved in his youngest son’s life, Bell was prone to fits of rage. He skipped class, picked fights with classmates and talked back to teachers.

In sixth grade, only a few weeks before summer break, Bell was expelled from Bancroft Middle School in Long Beach for one too many run-ins. After a year out of trouble at a charter school for students kicked out of the public school system, he transferred to Hughes, another public school in Long Beach.

It was during eighth grade at Hughes that Bell sprouted 4 inches, to 6-foot-5, and played organized basketball for the first time in several years. During elementary school, he had lost interest in the sport after his older brother, Josh — a skilled player three years his senior — had teased him relentlessly. Now, even as Bell looked better suited for a basketball court than a football field, he had designs on becoming the next Terrell Owens.

During summer practices with Long Beach Poly’s freshman football team, his phone and wallet were stolen from his locker. A friend singled out one of Bell’s teammates as the thief. One day, after a game outside San Diego, Bell found that player’s wallet unattended on the team bus. Hungry for a hot dog, he swiped the cash. It wasn’t long before the coaches found out and kicked him off the team.

“The good thing was that basketball season was right around the corner, and we had started practicing already,” Bell said. “I was like, ‘Well, at least I’ve still got something to do.’”

Bell flourished on the freshman team, but his grades lagged and his attitude problems persisted. In February 2010, toward the end of basketball season, he was removed from classes and placed in a program for students with behavioral issues called P.M. ACES. For the final 3½ months of the school year, Bell attended class from 2 to 6 p.m. in an annex behind the main building.

Metoyer monitored his progress, and after Bell was readmitted to mainstream classes for his sophomore year, the coach met with him and Gray. Thanks to his uncanny shot-blocking ability and size, Bell would skip junior varsity — provided he agree to several rules: maintain at least a 2.3 GPA; wear a tie and sweater to school on game days; and be on time to each class, practice and game.

Progress was slow. Whenever Bell trudged into practice late, mouthed off to a teacher or skipped a class, Metoyer retrieved a bag of seven dice he had confiscated from students. He rolled two to four dice at a time, depending on the severity of the infraction, and made the entire team run however many full-court wind sprints the dice dictated. On one particularly bad day, Metoyer had the team run 33.

By his junior season, the Jackrabbits were running on Bell’s account less and less often. It didn’t hurt that Metoyer started driving Bell to school in the morning toward the end of that year so that Gray could make the early shift at DPSS.

“If I got a bad report in class or something went wrong, that was the longest 10-minute ride of his life,” Metoyer said with a chuckle. “I was giving him an earful the entire ride, and I’m pretty sure he got tired of hearing it.”

Numerous hours spent strumming a plastic instrument in front of a TV screen have helped make Bell an elite shot-blocker. Because what the 6-8, 225-pound power forward lacks in length and height, he makes up for in timing.

“That comes from playing ‘Guitar Hero’ all the time,” Bell said. “No lie. You’ve got to hit the button at the same exact time, just like blocking a shot.”

Hardly a big-time scorer, Bell built his reputation on his mastery of the swat. In the summer entering his sophomore year at Long Beach Poly, after blocking 19 shots in an AAU game, he started receiving letters from high-major college programs. As a senior with the Jackrabbits, Bell cemented his blue-chip status with 4.8 blocks per game.

He considered joining Long Beach Poly teammate Roschon Prince at USC until his mom demanded he leave the Los Angeles area. The hope was that Bell, who was still relatively immature for his age, would grow up by going away to school.

Being on his own at Oregon forced him to be more accountable, and his relationship with his mother improved. One night early in his sophomore year, he called Gray to apologize. “Mom, I’m so sorry for everything I put you through in middle school and high school,” Bell told her. “I just didn’t know how good I had it.”

During his three years with the Ducks, Bell was an emotional leader for teams that won a combined 90 games, two Pac-12 regular-season titles and one conference tournament. This past spring, after his frontcourt sidekick Chris Boucher sustained an ACL tear in the Pac-12 tournament, Bell helped will Oregon deep into March Madness.

In the Ducks’ 74-60 win over top-seeded Kansas in the Elite Eight, he had 13 rebounds and eight blocks. Metoyer, who had arrived in Phoenix just hours before tip-off, embraced Bell in the stands before the Midwest Regional’s Most Valuable Player could even cut down the net.

A week later, after twice failing to box out in the waning seconds of a 77-76 loss to North Carolina in the Final Four, Bell, eyes red and cheeks puffy, fought back tears as he shouldered the brunt of the defeat.

“If I would have just boxed out, I had two opportunities to do it,” Bell told a swarm of reporters and cameras. “I missed both of them. We lost the game because of it.”

What most struck Gray and Metoyer watching the interview on TV was that, on the heels of the biggest loss in program history, he answered every question. It was a stark contrast from the childish teenager they once knew.

“That was pure Jordan Bell becoming a man,” Metoyer said. “I think Jordan Bell three or four years earlier would’ve blamed it on someone else. But the Jordan Bell you saw that night, that was a man that understood what accountability is.”

A couple of weeks after Bell agreed to a guaranteed two-year, $2.2 million deal with Golden State, he was honored at his family church, New Mount Calvary Baptist, in Los Angeles. Speaking to a crowd of familiar faces, he promised to take care of his mom.

Seven months earlier, at her home in Bellflower, Gray saw Bell perusing pictures online of rental homes in the neighboring, more affluent city of Lakewood. When she asked whether he planned to move there, he turned around and smiled.

“This is for you, Mom,” Bell said.

Gray moved this month into a new three-bedroom house.

Roughly 15 minutes have passed since Bell, microphone in hand, encouraged a large crowd of runners to “finish the race, even if you have to walk.” As dusk settles on San Francisco’s Mission Bay, the first racers near the final turn.

Bell, wearing a dark blue Warriors hoodie, signs a few autographs for race volunteers before stepping to the finish line to help hold a long blue banner. A young boy with braces who’s boxing up race T-shirts exclaims: “Jordan, I’m so glad we drafted you! You’re gonna kill it!”

When his agent called him on draft night to tell him Golden State had bought his rights, Bell’s disappointment over falling to the second round gave way to elation. Bell, whom the Warriors acquired largely for his defensive versatility, will get to play behind a player he has long emulated in Draymond Green.

Though Bell could crack the rotation as a rookie, he’ll have plenty of time to study under the Warriors’ cast of All-Stars. Now, after working out with Green, Kevin Durant and Klay Thompson at various points this summer, Bell is giddy about the prospect of finally meeting Stephen Curry.

“This whole thing is still a bit surreal for me,” Bell says. “Making the NBA was always the goal, but now that I’m actually here, it’s just, I don’t know. I’m just thankful I have the right people in my corner.”

Connor Letourneau is a San Francisco Chronicle staff writer. Email: cletourneau@sfchronicle.com. Twitter: @Con_Chron