Listen up, class. It's time to send our kids back to school. And as long as they're learning about presidents, percentages and punctuation, why not give them a lesson in protecting the planet?

Eco-friendly school supplies not only curtail landfill clutter and environmental toxins, they teach your campus-bound student the value of theother three R's: reduce, reuse and recycle. The greenest practice, of course, is to resist the urge — and the ads — to buy all new backpacks, notebooks and desk supplies. Dig through drawers to collect the vast stash of pencils, erasers and half-used spiral notebooks you already have. (If your kids need convincing, try calling that old pencil-sharpener "vintage," "retro" or "old school" instead of "used"!

No doubt you'll need new stuff, too, and finding low-impact brands can be tricky. So we've done the homework for you. Here are some back-to-school supplies that earn A's for green citizenship:

BACKPACKS

Steer clear of backpacks made with nylon or vinyl/PVC, which releases toxic dioxins during its manufacturing process. Instead, opt for earth-friendly fabrics like the organic hemp backpack from Rawganique,  or Quicksilver's organic cotton Republic, with a skateboard strap in front.

Voltaic bags are hot this season. Made from recycled soda bottles, these water-resistant backpacks have solar panels that will convert an hour of sunlight into three hours of iPod power.

PAPER PRODUCTS

The greenest paper products are chlorine-free, with high post-consumer waste content. One of our favorites is tree-free Banana Paper spiral-bound notebooks, made from the discarded stalks of banana trees.

But even Office Depot sells recycled notebook paper and its own brand of recycled notebooks, report covers and index cards these days.

PENS AND PENCILS

Remember when plastic pens were considered "disposable?" Refillable pens are easier on the environment, as are pens made from recycled plastic. Zebra makes a line of pens from recycled car headlights and CDs, and Pilot sells Be Green ballpoint and gel pens made from up to 81 percent recycled content.

Another low-profile option: A biodegradable pen made from cornstarch. It looks and works like a regular ballpoint, but disintegrates into the ground a year after you throw it away.

Wanna do the write thing? ForestChoice sells a pack of #2 graphite pencils certified by the Forest Stewardship Council as having come from ecologically well-managed forests. And Green Earth Office Supply peddles pencils made from recycled jeans, newspaper and even old money.

A final note: When your kid brings the teacher an apple this year, make it organic.