A few days ago I treated myself to a Lego WeDo construction set. I had been debating for a few months whether to buy it, but when I discovered that it could integrate with Scratch I felt that the decision was a bit of no-brainer so I went ahead and put in an order.
The box contains a variety of Lego pieces together with a: motor, distance sensor and tilt sensor which can all be connected to a computer via USB to be controlled. You can purchase some special software made by Lego to program your control systems, however I found that this wasn't really necessary since the familiar Scratch software lets you carry out pretty much the same tasks and also has the bonus of being free.
This helpful guide I downloaded describes what extra Scratch functionality is provided when the Lego WeDo controller is plugged in to your computer:
To say that I found it easy to control the motor using Scratch would be an understatement - all I had to do was double-click on a 'motor on' command block to get it moving and then double-click on a 'motor off' block to stop it again. The distance and tilt sensors were just as straightforward, with me getting Scratch to display their values on-screen using the 'Say' command block as I either moved the tilt sensor around or moved a pencil back and forth in front of the distance sensor to check that they were working.
The fun really started however when I began to incorporate them into some actual Lego models - not least due to the fact I had no instructions to follow since these are only supplied if you buy the Lego software and not when you just buy the bricks! My building skills didn't seem to mind the challenge of copying from some photographs I found on Flickr though, and I happily spent a good couple of hours building two models and creating two simple programs to control them using Scratch:
A Pair of Spinning Birds
A Hungry Alligator
As you can see, the results of my efforts were pretty good and I could definitely see the curriculum potential here since they required me to use loops and conditional (IF) statements to program an actuator (the motor) to work. I'm sure that children would love to learn how to complete their own similar projects themselves (presuming that they already had a little prior experience using Scratch) and would certainly find the task a lot more intuitive and exciting than other 'control' projects I've read about/delivered. I would highly recommend getting the set and would love to hear about anyone else's experiences of using it in the classroom.
Update January 2014 - Here is a guide on how to add the WeDo blocks in Scratch 2.0.