Each student held a handmade sign. The youthful handwriting and marker-inked pictures of penguins, turtles and polar bears belied the gravity of their message.

“Love your planet. Our life matters. Think about your life and children,” Edgartown School fifth grader Kahlia Nascimento’s sign said in Portuguese.

Students at the Edgartown School, Charter School, the regional high school, the Vineyard Montessori School and the West Tisbury school left their classrooms on Friday, joining the international walk-out to raise awareness about climate change. Students at the Chilmark School planned an after-school demonstration.

West Tisbury students joined the cause, first started by Greta Thunberg of Sweden. — Zoe Turcotte

At the Edgartown School, about 80 fifth and sixth graders lined Upper Main street along Cannonball Park, each holding a sign. Several expressed worries about rising sea levels.

“Half of Edgartown could be underwater. And that’s where I live,” said fifth grader Ruby Dellorusso.

Sophia Sampaio’s sign showed two pictures she drew of the earth: one looked familiar, the other was mostly blue ocean. “It’s a picture of the earth now and later if we don’t stop what we’re doing,” she said.

Fifth and sixth grade science teacher Kara Gelinas coordinated the school’s walkout. “I just couldn’t not,” she said. “I just feel like it trumps basically almost everything else, this issue.”

She said students were especially impressed after watching a video of teenage climate activist Greta Thunberg speaking at the United Nations climate conference. Ms. Thunberg has refused to go to school on Fridays since August, choosing instead to protest outside Swedish parliament demanding action on climate change. Her protest quickly drew attention and grew into an international movement with a worldwide walkout demonstration on Friday.

“I think they were floored by how clearly and articulately [Greta Thunberg] spoke as a high school student,” Ms. Gelinas said. “And the idea that she was just one person, and she actually did something.”

The future is concerned about their future. — Mark Alan Lovewell

The signs were as varied and colorful as the students who held them. One showed the earth melting over an ice cream cone with the words, “Make earth cool again.”

Others were more urgent: “Help children have a better future. Help stop climate change!!”

They called for a new future: “The earth is changing. Why can’t we?”

For many, daunting goals are tempered by daily actions. Fifth grader Georgia DeRoche said her family is working to reduce plastic use.

Starting early at the Chilmark School. — Rebekah Thomson

“The first thing we did is we’re not using plastic toothbrushes. We’re using bamboo toothbrushes. We’re also using soap bars instead of bottles of soap,” she said.

Some students started counting the supportive honks from adults in cars going by.

“We have 92. We’re going for 100,” said sixth grader Victor Valentin after about 25 minutes, underscoring both community support for the demonstration and Islanders’ reliance on fossil fuels.

“Millions of kids are doing this right now all across the world,” Ms. Gelinas told a group of students as she walked up the line.

“I want to chant right now,” said sixth grader Pedro Alves. “I want to chant that song from the civil rights movement, We Shall Overcome, you know?”