I highly recommend The Secret Science Alliance by Eleanor Davis. It's a graphic novel targeted at grades 3 and up. It's about 3 very different genius kids (Greta, Julian and Ben) who form an alliance to invent amazing things (and have to protect their inventions from a rival adult scientist). The message is great and the images are really fun. Here's a review: http://graphicnovelreporter.com/content/secret-science-alliance-and-copycat-crook-review