I am biased, since I develop conservation biology ed programs in NYC schools. BUT it's clear to me that the old adage is true:
" People will only conserve what they love; that they will only love what they understand; and that they will only understand what they are taught."

Why should anyone--adult or child--feel any urgency toward an abstract notion of the environment that means nothing to them personally or in their daily lives?

WE NEED TO GIVE KIDS DIRECT EXPERIENCE OF THE NATURAL WORLD. They need to understand that nature isn't something you see behind glass in a museum or zoo. That it exists all around us, even in cities. That their own lives depend heavily on natural systems and that nature is a joy and pleasure for all of us. Every human being--and every product, service and dollar of the economy--relies on a healthy environment. They need to understand that they are part of an incredible system with complex and marvelous interconnecting parts, most of which are alive. How cool is that?

Kids need to feel the same connection to the environment as they would to their home. If their house were burning down, you bet they'd be engaged, motivated and completely committed to learning how to put out the fire. It stops being an abstract, "do-good" luxury and something of vital personal importance.

But only if they experience it first hand. Unless kids feel that they are IN nature already, and not just studying it from outside,  top 10 lists will be worthless.

I agree somewhat with Beccane yet I also applaud your effots.  I have become involved with a group called Leave No Child Inside. You might want to check them out.  Even in the most urban of areas you can find nature. Also, I believe that students (and all of us) get involved when they feel a sense of ownership.  Look at what that man in Detroit has done with community gardens.  Maybe you could have the students start gardening somewhere at your school...even if it is only a windowsill.  It is good to know there are fellow educators like you!

I have had a fun time teaching local kids to pull invasive plants from the urban woodlands.  You would have to coordinate with whatever government group owns and maintains the property, but it is a great way to get kids outside, learning to ID invasive vs. native plants, educate them regarding the importance of planting only native plants.  You could also possibly arrange with your local government to do some tree/shrub planting.  Controlling invasives and restoring habitat for our native fauna are two very important tasks that will require the volunteer efforts of many hands and kids are already closer to the ground and have energy, hence less work for the old folks.  

I do a lot of watershed volunteer work and am jazzed about connecting people of all ages with the watershed they inhabit and depend on (and the nature it supports even in the middle of the city).  Check out your local streams and rivers, for some amazing discoveries, biology and  history.  We can positively influence and protect the health of our rivers and streams by many choices and behaviors.  Viewing the curb gutters as the headwater streams of this system is the real paradigm shift-- anything that is pollution there will be next in the river after a rainstorm.

We pick up trash in sensitive areas near the river, do stream walk education sessions in warm weather, and plant native tree and shrub seedlings to enhance the corridors along the streams (as well as the habitat in our own backyards).  Doing these things makes a tangible difference that people of all ages can feel and appreciate, and gives a sense of ownership and stewardship necessary if the problems of our globe are to be solved, one step at a time, by a series of very local actions that add up to sustainability.

People appreciate water because our bodies are made up mostly of it, and the tap water we depend on to drink comes often from surface water supplies (rivers and streams).  Kids appreciate swimming and fish, the other concepts of protection that the Clean Water Act pursues. EVERYONE lives in a watershed.

The US EPA's website allows you to "surf your watershed".  Find a local watershed group and get involved! Bring your kids and bring the message to families and folks of all ages.  Special educational events can be planned to learn about green roofs, rain gardens, backyard habitat, rain barrels, and other cool concepts.  Yes, you might expect to get your feet wet sometimes, but it's worth it.  

As an environmental educator, there are several things I make my students do.  On transportation, I tell them to plan a trip of over 10 miles that does not involve a car.  When they return their assignment, I tell them the next part-now go do it!  They got extra credit if they convinced a parent to go along.  For several it was their first trip on public transportation.  One group planned a Metrolink trip to the beach.  It was so successful that the next weekend a dozen other students also tried it.  Another is water usage.  They are told to monitor all of their water usage for 1 week.  Then they try to come up with ways to cut it.  They are also challenged to take the shortest showers.  With teenagers, this is quite an accomplishment.  They are used to 30+ minute showers.  When we do river testing for various chemicals, the best part is getting the students out to the riparian areas.  They absolutely love hiking through and around rivers.  Its an added bonus.

Scary title and maybe overboard. But somewhere, young people need to hear that it is the overpopulation of the human race that is responsible for the environmental mayhem that is ocurring today. Every student should read and discuss Quinn's novel, Ishmael. Not even Grist or Sierra Club or Greenpeace or Obama promotes a population plan. They won't even address the issue. But each of us needs to understand that there are too many of us.
 How many carbon credits should one be given for not having a child? I don't know but it's more than bringing one's own bag to the grocery store, or riding a bicycle or drinking tap water.

Teach the kids how to write to political and business leaders. The Kid's Guide to Social Action by Barbara Lewis is a great intro for kids (and adults!) to letters, petitions, publicity, etc.