When Janet Fillion started teaching eighth grade Latin at Boston Latin Academy — then called Girls Latin — in 1970, she had just turned 22 years old. The other teachers often mistook her for a student.

“There were a lot of older teachers — which I guess I shouldn't look askance at right now, ‘cause I'm one of them — but they thought I was one of the kids,” Fillion said.

Fillion has weathered every change that's faced the school throughout her nearly 50-year-long career. Now, she has decided this will be her final year teaching, she told WGBH News.

She credits the long career to her role as the fearless leader of the Classics Club, which is a deep dive into all things ancient Rome, from chariot races to toga contests to translating Latin at national competitions.

“That's really why I've stayed as long as I have," Fillion said. "Because we do so many fun things and I love it, and I love the energy of the club. It's mostly done after school, on weekends and in the summer. It's a full-year job that we do.”

Back when Fillion was still the new kid among the teachers, she took a novel approach to her lessons: teaching Latin declensions with song. Her debut was “Mexican Hat Sum,” a riff on the Mexican Hat Dance by declining the verb for “I am” in Latin. And what worked back then still works today, she found.

“It was originally just that one song, and now I have countless. I keep thinking I'm going to make a YouTube, but I haven't,” she said.

Fillion's love of the classics hasn’t diminished after decades of teaching eighth-graders how to decline nouns and conjugate verbs. If anything, it’s grown. When asked to elaborate on the value of learning Latin, she said, almost exasperatedly, "Well, it's the basis of our culture, actually."

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A yearbook photo of Janet Fillion from her first year of teaching at Girls Latin, now Boston Latin Academy, in 1970.
Cristina Quinn WGBH News

“Sixty-five percent of our words are from ancient Latin and Greek. And if you understand derivatives and roots of words, you can understand a word you may never have seen before because it will have a Latin root in it,” she said. “But also, I've always liked the fact that it's very patterned and it's sort of mathematical. And I think it's good for the brain.”

Fillion has taught thousands of students in her career. In that span, she has been teaching for every cultural and technological milestone, including the arrival of smartphones and social media, but she said all that hasn't really changed the classroom.

“Phones have changed them, in one sense. But I mean, they’re still the same wonderful, cute kids — and some very exasperating ones,” she said. “What I like about children is when they're earnest — just like people! When they really try and they want to do better.”

Her enthusiasm is so infectious, it inspired her former student, Viet Luong, to follow in her footsteps.

“I could tell how much she loves Latin and how much she also loves the kids. And so, that's one of the reasons why I got into teaching, too,” Luong said.

"She actually got me involved in the Classics Club when I was in my ninth grade," she said. "I was so involved, I became a student leader for the club. And then I just ended up really enjoying the experience, and I wanted to become a Latin teacher so I can inspire my students."

Luong, who refers to Fillion as the "OG" — the "original gangster" — of the Latin department, has also been teaching at Latin Academy for 11 years. She’s even penned her own Latin declension songs, but insists Fillion’s are hard to top.

“I always steal hers. Hers are really good. And then when my students get passed on to her, they come back to me and say, ‘Ms. Fillion is doing the same songs!’ And I say, ‘You know, I stole it from my old Latin teacher.'”

Another student Fillion had a lasting impression on is this reporter. I was an earnest eighth-grader who found Ms. Fillion tough but fair. And her songs were, indeed, catchy. Unfortunately, I'm a bit rusty, but I remember most of "Mexican Hat Sum" and quickly joined in when she prompted me.

After our duet, I asked if she feels ready for retirement.

"No and yes. No and yes," she repeated. Every now and then, she said, her voice gets a little tired.

"I don't mean my singing voice. I mean, just my voice is not as good, and so sometimes I actually get tired of speaking even by the end of one class," she said.

But she's not discouraged. When asked what she's looking forward to doing in retirement, she quickly responded: "Trying to find a volunteer job where I can teach."