On the last day of the only job he’s known for three decades, Dean Howarth wore a kilt.

It was the same kilt he’d worn for many first days of school, a purchase inspired by his travels to Scotland years ago, which included a visit to Duart Castle — the ancestral home of the Clan Maclean. A fitting homage, he thought, for his final hours as a physics teacher at McLean High School in Fairfax County.

“Highlander pride, to the end,” he explained, invoking the high school’s mascot.

When Howarth began teaching in 1987, teachers mingled in a smoking lounge, and copies were cranked out on a mimeograph. He was a bespectacled 22-year-old, fresh out of Virginia Tech, not much older than the teenagers he taught, when The Washington Post chronicled his rookie year as a high school physics teacher.

“My idealism hasn’t been crushed,” he told The Post at the end of his first year. “I still think I have a lot to offer.”

Howarth plans to teach at a private school in the District’s Chevy Chase neighborhood next year, his departure from McLean motivated, in part, by frustrations over testing demands and stagnant teacher wages. But also because 30 years feels like a natural denouement.

His career at McLean behind him, “balder and thick around the middle,” Howarth has a word or two — or many — to say about the state of his profession. Much of it isn’t complimentary, and most of it has to do with what he deems the “AP-ization” of education.

Too much of education, he said, has become about teaching to a test. In Virginia, he said, it began with the arrival of the Standards of Learning exams, assessments students must pass to graduate. These days, he quipped, students would enroll in Advanced Placement “snake handling” if they knew it would burnish their transcripts.

Yes, Howarth said, tests teach rigor and scholarship and dedication. But, used as a measure of achievement, they can also perpetuate an all-or-nothing mentality, he said.

Success is more subtle, less quantifiable. For Howarth, it’s a glint in a student’s eye, a hand that shoots into the air a beat faster, signaling a question.

“People hate this because it doesn’t have a rubric, and someone can’t come in and score it,” he said.

It’s why he has taught nearly every level of physics, from introductory to honors, but not AP. He considers himself fortunate he wasn’t burdened by the same state testing demands as colleagues who teach biology and chemistry — unlike those subjects, there is no physics Standards of Learning test.

Then, there are the loathsome buzzwords, drummed up by educational consultants whom Howarth accuses of trying to score a buck.

“Don’t get me started,” he said, leaning back in a chair inside his classroom one afternoon. “I make a conscious effort to purge them from my mind.”

There’s “data-driven analysis” and “disaggregation” and, his fingers forming air quotes, “granular approach” — concepts, Howarth said, that encourage a one-size-fits-all approach to education when a classroom should be a “crucible of experimentation.” Good ideas, he said, lost in the blather.

“Teaching, fundamentally, is a simple thing,” he said. “Some people who know stuff try to get people who don’t know it to understand it.”

Howarth tried to take after Carl Sagan, an astronomer he admired for taking an esoteric discipline and relating it to the human experience.

“Sure, people think, like, ‘Oh, I love art because it speaks to me.’ Well, I think physics can speak to you, too,” he said. “There’s the same elegance and beauty hiding in the stars or in equations.”

Howarth did away with textbooks about a decade ago, reasoning that teaching physics with a tennis ball and racket, or a rubber band, was far more memorable. He changed the way he graded students, declining to penalize teenagers who didn’t turn in homework but aced tests.

He’s lain atop a bed of nails to teach about pressure. He’s had students build catapults and launch pumpkins as they studied projectile motion.

There’s little about his career Howarth said he would have done differently. But, if he were to give advice to his younger self, he would have offered this assurance: “When you’ve stood your ground, it will pay off.”

The headline in The Post on Sept. 9, 1987, when readers were introduced to Howarth, declared, “Teacher Starts Off Job With Zest.” He was entering the profession as “higher salaries and national concern about the quality of education have raised the status of teaching after years of benign neglect,” according to the article.

At the end of Howarth’s first school year, in 1988, he told The Post that he hoped a few years down the road — when he was 33 — he could still relate to students. All these years later, and he still views the bond between student and teacher as a sacred covenant.

“I don’t know what the trick is,” he said. “It might be that I’m still a kid at heart.”

To McLean students, Howarth was an animating force. Homework assignments included illustrations of Galileo, Isaac Newton and Albert Einstein, recalled Raphael Perrino, who graduated in 2003.

Perrino wrote a letter supporting a resolution passed by the Fairfax County School Board to rename the observatory at McLean after Howarth. The teacher was instrumental in refurbishing the observatory.

“He finds a way to bring humor, life, enjoyment into everything that he teaches,” Perrino said at the renaming ceremony. “You’re dealing with really serious topics. You’re dealing with the mathematical nature of the universe. But he’s doing it in a way to kind of bring kids in.”

Glowing reviews speckle his Ratemyteachers.com page.

“Best person I’ve ever met, not only as a teacher but also as a human being,” read one.

“Honest, trustworthy and genuine,” read another.

He led a historical reenactment club after hours, helping students plan their costumes and develop characters with great care, said another graduate, Abigail Fine, 30.

“He’s certainly more dedicated and passionate about after-school activities than any teacher I’ve ever met,” she said. “There are very few teachers that are dedicated enough to stay.”

To colleagues, he was a steadying presence.

“Veteran teachers look to him as a leader, and the newer teachers, coming in, go to him and seek advice,” McLean Principal Ellen Reilly said.

His last day of class at McLean in June passed quietly. Some wall hangings remained, as did the mural he painted years ago of Urania, the Greek muse of astronomy. But most of his belongings had been packed into boxes and moved, his desk emptied.

High school seniors had already graduated, and only a handful of underclassmen trickled in for the abbreviated school day. Former students stopped by to wish Howarth well, including some who loitered until the final bell. He signed yearbooks, offered to write letters of recommendation for promising students and projected a clip of the movie “Ferris Bueller’s Day Off” onto the whiteboard.

“Thank you for impacting my life,” one girl told him.

Howarth wants to stop teaching, for good by 2026, and watch World Cup games from the stands when the United States co-hosts the event.

Eventually, he would like to traverse by train the “science capitals” of the world — Einstein’s German home town, the site in Italy where Galileo’s remains rest, for instance.

“Wouldn’t that be nice?” Howarth said. “Just be a student of the globe.”