Like last months Earth Hour, the coming of Earth Day is a great way to teach about recycling, the environment and create an awareness about energy usage and pollution.
Around here a favorite thing to do is the garbage walk. Bring gloves and garbage bags, but take these things to your favorite park and walk the edge of the woods with your kids. Pick up stray bits of garbage that have either been littered or blown in on the wind... This helps teach an awareness of the growth and cycles of the Earth, plus what leaving all that mess about does to it.
As plants are growing more and the planet is greening up – at least here in the northern hemisphere, this is also a good time to take out the string and ruler and mark the growth of the plants you looked at last month.
If you have Willow trees near – now is a great time to mark a spot on a low hanging branch to watch and record it's growth as well, and then use that as a spring board for teaching how Willow trees need water in abundance and that they can be used as a marker for not only the volume of water in the ground but for the quality of the water. Granted it can not be used as the only marker, but is a good indicator of the water being healthy if the tree is healthy.
What lessons do you let nature teach your students (other than 'leaves of three, let them be')?