Joe Dale has been making a lot of use of these in languages for some time, and I used to use them for homeworks and a few other things in my previous teaching job, particularly with 6th form groups, although they are now just as likely to be used lower down the school as well. Useful article HERE.
I'll be making use of QR codes to add extra options for some of the work that students are doing.
Here's a useful guide to what QR codes are from Jon Tait.
Here's the first QR code to go up on the classroom walls... the first of many...
