He worked as an elementary school’s janitor for 27 years, then one day, he became its principal

Joseph "Gabe" Sonnier's story is a lesson in perseverance. It began in 1985 when Westley Jones — the then-principal of Port Barre Elementary in Port Barre, Louisiana — pulled Sonnier aside one day and shared his vision for the janitor's future. "He said, 'Being a janitor is a good job and it's an honest living,'" Sonnier told PEOPLE. "'But I taught you unlimited potential. I think you'd benefit the students better as an educator. I'd rather see you grading papers than picking them up.'" Fifteen years later, Sonnier took Jones's advice. At the age of 39, he went back to school while still working full-time.

He put himself through a grueling schedule to achieve his goal. Arriving at Port Barre Elementary at 5 a.m., Sonnier would work until 7 a.m. and then go to classes at Louisiana State University Eunice and the University of Louisiana. After he was done with his night classes, he'd often return to work. "I'd finish there and then go home and do homework," he recalled. "It was hardly much rest." Sonnier's hard work and determination eventually paid off. In 2006, he graduated with an associate's degree in general studies from Louisiana State University Eunice, and two years later, he received a bachelor's degree in elementary education from the University of Louisiana.

A master's degree followed, and then in November 2013, Sonnier became principal of the same school he'd cleaned for 27 years. "Who would have thought 33 years ago, when I set foot on this campus, that I'd eventually be the leader of this school?" he remarked. Sonnier explained that although he had always planned to go to college right after high school, family circumstances had prevented him from continuing his education. "After my first semester, I had to drop out because my mother and father were separating," he recalled. "My mother was a housekeeper and she needed help with the bills, so I went into the workforce. I was going to do anything to help my mom."

Sonnier took up jobs in construction, at a grocery store, and a sawmill before eventually starting work at Port Barre Elementary as a janitor — a job that his father had held for most of his life. "When I first started, it was my intention to work five, maybe 10 years as a janitor and then look to do something else," he said. This, however, almost turned into 20 before Jones's fateful comment became the push he needed. "The seed was planted in my heart and my mind," said Sonnier.

He admitted that his role as the principal only "really sunk in" after he held his first staff meeting. "I had an entire staff wanting to know my expectations of them as a leader. I know this job can be overwhelming at times, but I take one detail or one thing at a time," said Sonnier. His success also inspired five other staffers to earn their own master's degrees. "Sometimes it felt like too much and I'd want to quit," one of them, kindergarten teacher Tonya Stelly, said. "But he always had encouraging words. He'd say, 'Just stick with it. It'll be worth it in the long run.'"

Sharing some advice for those who feel stuck in difficult situations, Sonnier told CBS News: "Don't let your situation that you're in now define what you're going to become later. I always tell them it's not where you start, it's how you finish."