I have been teaching 6th through 8th graders Processing (processing.org). They love the creative, visual aspect of it. It's essentially Java, with a layer of ease so you can very quickly get things done. The quick code-run-tweak cycles are an advantage (similar to Scratch in that respect). Because it's Java, all the programming fundamentals (functions, variables, loops, branching, objects) can be taught - but with the purpose of creating something interesting. There are a number of tutorials and books available for teaching (see www.learningprocessing.com), and you can code entirely online at sketchpad.cc.