If you have students who finish classwork early you can have a classroom display in your class of a variety of different QR codes. The students can then take their mobile phones up to the QR codes and scan one. Once they scan the code they will be given an activity which you have already set up for them to try in class or even for homework.
You can place a QR code on the door of your classroom to give students or even perspective parents details and overviews of your lesson. Students can use a QR code to find out if there has been a room change.
Students can create their own QR code if they post something online. QR codes can be created at www.qrstuff.com or you can google QR Code Generators to find other websites which will do this for free.
If you want to create a sheet with revision topics or in classroom welcome packs you may also want to include a list of useful websites which you can give to your students in the form of a QR code.
It's a really fun way to get the students engaged in doing additional work and bringing the use of technology into the EAL classroom.