He'd have his students unload their weapons before gym class and promised to return everything once the bell sounded. In his first year, he said he broke up a fight and inadvertently took a knife slash to the right jaw. He needed seven stitches and still has the scar. After that, his principal gave him a piece of advice: Act once the fight has ended.
"I learned that lesson very quickly," he said.
He coached baseball with one bat and ball - for fear his players would hit each other with any extra equipment. The experience changed his life.
"You learned about how to talk to people," he said. "How to show compassion to people."
After three years, he moved to Antelope Valley College in Los Angeles County and spent five seasons coaching junior college players. It's where he formed his mantra: "Be on time. Be professional. Respect the game."
It's also where he established a reputation for treating every player the same - even if they weren't on his club.
Jim Slaton, a veteran major league pitcher, would spend his winters working out at Antelope Valley because it was near his offseason home. Once, Slaton left his glove on the field after practice.
The next day, Trembley gathered his team, held up Slaton's glove and then held up his other hand and said, "Slate, that's five."
"Five laps around the field. And I took off running," said Slaton, now the Seattle Mariners' bullpen coach. "All his players just loved it. Now whenever I see him, I hold up my hand and say, `That's five.'"
Marty Reed is the first of a long list of players whose baseball careers Trembley saved.
In 1984, Trembley left Antelope Valley for a $300-per-week job working in the Florida Instructional League for the Chicago Cubs. Within two years he was asked to manage a co-op team in Kinston, N.C., a Single-A Carolina League club made up of players from four organizations. The California Angels sent Reed, a 24-year-old pitcher in his third year of pro ball.
In the team's first meeting, Trembley, who was the club's only coach, told the players they were there because no one else wanted them. But he promised to make them better.
Reed, a starter, had a disastrous April, going 0-3 with a 12.58 ERA. The day after a terrible start he sat by himself at the end of the bench pondering whether he should quit baseball.
Trembley joined Reed and said he'd still get the ball every fifth day if he vowed to work hard. Reed agreed, and took off after that pep talk, going 16-3 for the remainder of the season and finishing with a 3.10 ERA.
In August, the Angels asked Reed to go to another Single-A team for a playoff push, but he declined - so he could finish the year with Trembley.
"Here is a guy that did something tremendous for me and I can't walk away from him," said Reed, who eventually pitched in Triple-A and is now the Dodgers' minor league pitching coordinator. "I was at a crossroads in my life, and this guy has a knack for making you believe in yourself."
The next year Trembley landed a job with the Double-A Harrisburg Senators in the Pittsburgh Pirates' organization. After a rough start, he led the team to an Eastern League title, earning the first of his three Manager of the Year honors in the minors.
It's where he met Venezuelan infielder Carlos Garcia, who was in his second year of pro ball. Garcia remembers not running out a ground ball and being confronted by Trembley. He told the kid he had the talent to make the majors, but he had to work at it.
"That was enough for me," said Garcia, who spent 10 seasons in the majors and made one All-Star team. "He was the first guy to give me that kind of confidence."
Earlier this year, Garcia, the Mariners' third base coach, saw Trembley at Safeco Field. They embraced, and tears filled Garcia's eyes.
"It was pretty emotional, but I love Dave and I am happy he got this opportunity," he said.
From a bus to a buss
For two decades, Trembley rode the minor league carousel. He nurtured players and watched them rise while his ceiling held steady.
A dozen stops. Sixteen straight years of never making more than $35,000 annually, managing 2,800 minor league games, not including playoffs, spring training, instructional league and winter ball in places like Mexico or Venezuela.
He put more than 225,000 miles on his 1973 Datsun hatchback. For more than a decade he used a post office box to get his mail and a storage facility to hold his valuables since he was never in one place for more than a few months. Sometimes, after winter ball and before spring training, he'd live on friends' couches.
"The minor leagues are no picnic. I was eating peanut butter and jelly sandwiches," Trembley said. "There were a lot of things you couldn't do, a lot of places you couldn't go because you didn't have any money.
"I had to work for everything I've gotten. And I know what it's like in the minor leagues. In the minor leagues, as a player and a prospect they try to beat you down. They try to find out what you can't do, not what you can do."