Connor has been learning Scratch and playing with it for about 9 months now. I am working hard to keep him challenged and find great projects for the other students in my class that have already taken intro to Scratch.
Here are some nifty Advanced Scratch resources:
Buy the book "Scratch for Teens"
A website with Scratch Challenges
Coder Dojo Anthenry has some great projects too!
If this isn't enough look into Scratch and Enchantment (with LEGO mindstorms) or Makey Makey or Raspberry Pi.