YARMOUTH — Before the fourth-graders walked into the music room Wednesday, Karen Renton seemed more excited to be one class away from summer vacation than emotional about coming to the end of her 34-year career.

“I have a smile that just doesn’t stop today,” she said.

But that would change.

At 10:20 a.m., the students started trickling into the room at Yarmouth Elementary School where Renton has taught for all but two years of her career.

“Hello, my friends. Come in, come in,” she said, as they took seats on the edges of a big blue rug with a treble clef in the center.

Renton, 55, thought she was going to be a marine biologist until her senior year at Edward Little High School in Auburn. That’s when the flute and piccolo player started favoring music over science.

“You know how they talk about significant people in your lives?” she said. The band director was hers.

She aspired to follow her mentor’s career path, complete with summers off, and studied music education at the University of New Hampshire.

Renton’s first job was in the Sacopee Valley School District, where she was the sole music teacher for kindergarten to seventh-grade students from Hiram and four other western Maine towns.

“I was burning fast,” she said of having to go between the district’s seven schools.

She also was dating a man based at the Brunswick Naval Air Station – “one of those Navy guys that my grandmother told me to look out for,” she said – and wanted to be closer to him. When a fellow music teacher she had met in a summer class told her she was leaving her job in Yarmouth, Renton – then Karen Mary Tassinari – made sure to apply.

The superintendent was concerned that she didn’t play the piano. And although she sang as a kid, her brothers had teased her out of ever joining a chorus. The job would require her to lead one.

Still, the principal and music teacher from Yarmouth came to observe her class.

“I had them dancing with first-graders,” Renton said. She thinks that’s what got her the job.

MAKING AN IMPACT, ENDING A CAREER

Since then, Renton has worked for five principals and four superintendents. Fifteen years ago, she petitioned for a window in her room, the hottest in the school, and got it. She developed a curriculum around her guitar, which she named Gretchen, taught the stories of the great composers, and got kids who were convinced they were bad at music to read notes from a page and play them on the recorder.

She has received letters from former students reminiscing about all of it, and notes from others who remember something more.

There is one letter in particular that chokes up Renton when she thinks of it. It came from a student who never stood out, but wanted to let her know that her class made him feel safe.

“That’s what it’s all about,” she said. “That’s what makes the difference.”

At some point along the way, Renton married that Navy guy, who’s 10 years her senior. Their plan has always been for her to retire when he turned 65.

“Everybody always says, ‘You’ll know when you’re ready,’ ” she said, and this year, she did.

In the fall, when she and her husband came across a two-week cruise that leaves for the Caribbean at the end of October, she had to make a decision.

“Finally, my husband said, ‘Let’s book it,’ ” she said.

As Renton started her last week of classes, she still didn’t think it would hit her until school started in September without her. She remained unfazed through most of her last class.

As she strummed Gretchen’s strings, the students sang along, then sat quietly, some with their heads buried in their knees, as she read the last chapter from a book about Beethoven.

They grabbed xylophones and glockenspiels from the shelves to play along to “Ode to Joy,” following the red dot from Renton’s laser pointer that jumped from note to note on the sheet music projected on a screen in front of the class.

MUSICAL FINALE WITH MEANING

Near the end of the period, she got out yellow plastic cups for a game she’d been using to teach rhythm to children long before actress Anna Kendrick popularized it in the movie “Pitch Perfect.”

Sitting at the front of the room, Renton led the class through a song playing from her iPod, clapping, tapping on the cup, picking it up and tossing it in the air.

Then she played a video of four teenagers replicating Kendrick’s cup percussion to her remake of the Carter Family song “When I’m Gone.”

Moving through the classroom, she sat down with clusters of kids as they tried to tap the cups to the beat, some girls performing it by heart, while others, with the end of the school year moments away, barely sitting up.

Through the song, Renton’s encouraging smile was focused on the children, until it came to the last lyric, when she turned toward the teens on the projector, her lips pursed.

They sang, “You’re gonna miss me when I’m gone.”