How about origami? I had a collegue of mine who worked with kids about that age and that was the tool she used. A simple book will have easy and harder designs to make. It will teach him all kinds of skills like self control, progressing in a sequential fashion towards an end, and give him a sense of mastery to build his self-esteem.

Books are easy to come by or find at the library, and all you need is some thin paper.
Hope this helps!!

Laura G

Lead the kids in a play with hand puppets.
Study a book on Origami then teach it to the others.
You can make some bean bags (split peas in a ziplock bag, then a second ziplock bag to make sure they stay sealed. Practice juggling. Two kids two bags and play catch. Masking tape on the floor to make targets.
Find a library book on science experiments.
Have him develop art work to show the various kinds of clouds, the stages of an insects life, parts of a plant, the solar system, etc.
Draw the set for a scene from a movie or story.
Have him set up interviews to get statistics and do charts that show what he learned from the other kids. The topic could be: things you recycle, what you eat for breakfast, TV shows you watch or things that make you smile/laugh/cry or mad.
Give him flash cards to help other kids study the basics.
Class project to make 2013 calendars for Christmas presents.

Great suggestions that can always be used!

Just wanted to make you aware that this thread was started in 2009 so don't be surprised if you don't hear back from the original poster.

And the 12 yr old is now 15...LOL!!

Kids grow up fast, don't they?