Scratch is freely-available interactive multimedia educational software from the Massachusetts Institute of Technology. It is intended to teach basic computer programming  concepts using simple manipulations of graphics, images and shapes.

 

Here's a very good introductory article about Scratch (from Communications of the ACM, Vol 52, pages 60-67).

 

If you're running into problems installing Scratch on your school's computers, this article by Roger Davies (Queen Elizabeth School, Cumbria) may help you along.

 

• view Scratch screenshot.

Scratch is available as a free download from scratch.mit.edu, where you can also find teaching materials and tutorials.

 

Download Scratch.