When some 20 million people participated in protests, teach-ins, and other activities on the first Earth Day, April 22, 1970, there was no World Wide Web. Today, the Internet helps link people worldwide who want to protect the earth's environment and its creatures, share what they are learning, and take group action — and your kids can participate.

But when it comes to tending the planet, every day is really Earth Day. The Rainforest Action Network, like many environmental groups on the Web, provides "Action Alerts." You can also pick out an environmental issue close to home and organize a letter-writing effort to your local member of the U.S. House of Representatives.

The animal world is well-represented on the Web, with countless sites devoted to particular animals and saving endangered species. The Tiger Information Center, for instance, offers your students a chance to learn about the threats of poaching and other human activities to tigers and what people can do about it. Or ask your students to pick their own favorite animal or plant — surely, there will be a Web site devoted to it!