I've tried several educational programming environments for a semester at a time, and Scratch is by far the best for students too young to type. Logo and Proces

I've tried several educational programming environments for a semester at a time, and Scratch is by far the best for students too young to type. Logo and Processing are nice for slightly older students. It's not immediately obvious, but Scratch is very very good at some important things for education. Loading, saving, and starting the editor are fast even on slow machines. When things go wrong, they don't stop the rest of the program. And concurrent programs are easy to write in a wide range of styles because multi-frame loops run at exactly the same speed for all scripts. There are a lot of imitators that improve on Scratch's weaknesses by adding first-class references to lists, sprites, and functions. Or integrating a physics engine. Or binding directly to Minecraft or Sphero. But if they are slow to load or execute, you can't iterate as many times in an hour of class. If errors demand time to troubleshoot, that attention comes out of the rest of the class's instructor time. If you are limited to only one way of writing concurrent processes, it might not be a style that fits well with a particular lesson. I hope that the ongoing HTML5 port of Scratch gets the same things right.