I strongly agree with you about making concepts concrete. I have been working with a couple of groups who are using Scratch, and they are having great success. One friend in particular finds young people really like physical interaction, she is using 'real' picoboards.
What age range are you using Scratch with?
I realise this is about mbed, but I have an experimental implementation of the picoboard/Scratch sensor board firmware for Arduino/Freeduino too. Would that be of use? I could clean it up and release that. It needs sensors to be plugged in, but that can be done with veroboard. Arduino has the nice property that they are cheap (£14 for Freeduino).
GB-)
I'm interested in the work done on the interfacing of mbed to the Scratch programming environment. I don't know who developed the Scratch.bin program which interfaces with the Scratch enrvironment but is the source code available for this?
John Stout