It was a moment that reminded Glen Greenfield why he got into education in the first place.

Last year, the Lincoln Middle School history teacher ran into a former student who was in his junior year at Santa Monica High School. The student had just enrolled in an Advanced Placement history course.

“He told me that on the first day of class the teacher asked all 29 students why they were taking AP history and 13 of the students said, ‘Because of Mr. Greenfield,’” he said. “That gave me more joy than you can imagine. As teachers, we don’t often get the opportunity to see how our efforts might impact students later in life.”

Greenfield’s efforts will probably impact students even after he’s done teaching in the Santa Monica-Malibu school district, a milestone that is quickly approaching. At the end of the school year, he will finish his tenure at the California Avenue campus he’s worked at for 23 years.

He’s never taught anywhere else.

“I have absolutely no regrets about my teacher career,” he said. “The kids have been great, enthusiastic and eager to learn. The parents have been supportive, and the staff at Lincoln have been great to work with.”

Born and raised in Los Angeles, Greenfield attended Evergreen State College in Washington state before transferring to UCLA. But he didn’t go into education right away.

Greenfield worked in advertising for a few years and then got involved in the import industry, launching his own wine company before selling his stake to his business partner. He then went back to school, earning his teaching credential at Cal State Northridge.

From a young age, Greenfield was interested in history and politics. He walked a precinct with his father in support of John F. Kennedy when he was 7 years old, and he dreamed of becoming the first Jewish president.

Later, as he looked for work in education, Greenfield was impressed by what he saw at Lincoln.

“It was the only school I had visited that was actually doing the in-depth quality teaching that we learned about in our college courses,” he said.

For his audition at the California Avenue school, he taught an 8th-grade English class as the principal, vice principal and two teachers observed. He then led a 6th-grade history lesson. He got the job, eventually becoming a fixture as an 8th-grade history teacher.

Greenfield was briefly a counselor at Lincoln returned to the classroom after four years, saying he missed teaching too much.

“My greatest challenge as a teacher is also the most fun — helping students to be able to understand and articulate both sides of an issue,” he said. “If it’s the Civil War or the American Revolution or whatever, there are two sides to every event. And no matter what you believe, you should at least be able to understand the other side’s point of view.

“This is quite a challenge for them when we are discussing current events and the students are asked to defend, as an intellectual exercise, a point of view they don’t agree with.”

In retirement, Greenfield plans to add to his triathlon resume. He often wakes up at 5 a.m. to run or ride his bike before school, and he’s participated in the Malibu Triathlon, among others.

Greenfield said he also wants to volunteer with Court Appointed Special Advocates (CASA), a nonprofit organization that helps foster children.

This year, Greenfield’s last in SMMUSD, he is on the same campus as his 6th-grade daughter. And that’s not the only reason why next year will require some adapting on his part.

“I’m a little nervous about retiring,” he said. “I get a lot of gratification from teaching, and I know I’ll miss it.”