Invisibles Question

From PLC member Bobbi Roblido:

Hi Ben,

Got your book The Easy Way yesterday and am devouring it as quickly as possible! I want to plant some Invisibles on my back wall to start including some indirectly in our stories, subtly as you suggest. I know I have seen a gallery of them somewhere but have no idea where. Can you point me in the right direction?

Also, have any elementary teachers chimed in on the effectiveness of going this route with the younger kids? I am thinking I could go as low as 4th grade, but doubt that my 2nd graders or 3rd graders would have the artistic ability yet.

Thanks!
Bobbi