Here are a couple of wonderful free resources for homeschoolers who want to start nature journaling with their kids.

Nature artist and educator John Muir Laws is offering free downloads of his nature journaling book, How to Teach Nature Journaling and his curriculum, Opening the World through Journaling: Integrating art, science, and language arts, absolutely free on his website.
How to Teach Nature Journaling is a comprehensive guide for educators, parents and those who wish to mentor others to develop nature journaling skills. It is available both as a printed book and a free PDF download. He welcomes donations to help him continue his work, too. Order or download it here.
The curriculum, Opening the World through Journaling: Integrating art, science, and language arts, is also available as a free download. Download the curriculum here. Laws says that it is geared primarily towards children age 8 and up (specifically grades 3 through 7) but works just as well for teenagers and adults.
The curriculum includes activities like drawing and writing about plants and animals in the field, poetry writing, games, making treasure maps, keeping a field journal and much more.
Note that you do have to fill out your name and email to download the materials when you check out, but you do not have to fill out any billing information if your order is free and you do not make a donation. Your downloads will be immediately available on the next screen when you check out.
Laws also maintains a How to Teach Nature Journaling Facebook Group that parents and teachers are welcome to join.

For another free nature journaling resource, you can print out my own non-profit monthly nature education magazine, Wild Kids Magazine, which I’ve been publishing online for over six years. Wild Kids generally includes nature activities, foraging info, nature journaling pages, seasonal poetry, botanical coloring pages, in depth info on wild plants, educational nature games and more. It is also a PDF and can be read online or printed.

