According to the Common Core standards for writing, elementary-aged students should be able to write pieces that state and give reasons to support an idea. They can celebrate Earth Day and practice these skills by writing about something they can do to help the environment and making an action plan to accomplish it. For example, a student might write about how he wants to recycle more at home and will do this by taking juice boxes, paper and cans to the nearest recycling bin instead of throwing them in the trash.
Along with Gaylord Nelson, the founder of Earth Day, history is full of environmental activists who left a lasting impact on the movement toward a healthier earth. The educational resources website "Read Write Think" suggests having students write reports about pioneering environmentalists. These essays can describe the person's life, significant accomplishments, and a lesson they teach about caring for the planet. For example, a student might write about scientist George Washington Carver, who invented new uses for the peanut and pioneered practices like crop rotation and composting.
One way to both practice student writing skills and make Earth Day relevant to students' lives is to have them investigate environmental issues currently taking place on school property. As a class, you can go on a conservation walk around school property, keeping your eyes open for issues that could need attention. For example, there might be a leaky faucet in the bathroom, or littering could be rampant on the playground. They can then write essays that describe one of the problems they observed and suggest a solution.
From Shel Silverstein's "The Giving Tree" to Dr. Seuss's "The Lorax," children's books are full of fictional environmentalist characters. One approach to the Earth Day essay is to have students write descriptive essays about their favorite Earth-saving protagonists. Using examples from the book, they can describe what part of the Earth the character cares about and what he does to protect it. For example, a student might write about the Lorax's passion for the plight of the Truffula trees and how he isn't afraid to speak out, even when his efforts are dismissed or ignored.