Visiting MSR/Bangalore I was shown a neat demo using very simple QRcode-like paper and image recognition. Basically, each student had a paper they could hold up. On the front was a simple QR-code (facing the prof and camera). On the back on the edges were 4 possible answers, something like A/1/YES, B/2/NO, C/3/MAYBE, D/4/DONT-KNOW. The student would rotate the paper so their chosen answer was on top, then hold it up. A camera in the front of the room would detect in realtime and display the results. They even had an augmented reality smartphone app that would cover/highlight the students and their responses.
Oh, and the QR codes were per student, so answers could be tracked.
I'm not sure what scale you mean. The demo I saw involved 100+ students in a crowded low-income rural Indian classroom with one teacher. The qrcodes were printed on regular paper on an inkjet printer. The image recognition software ran entirely on a cheap desktop with a webcam. The whole thing was designed for that type of environment.
I doubt it will be used much -- teachers who care seemed to be in even shorter supply than the minimal tech needed to run this -- but the guys at MSR that created it had put an surprising amount of work into making the image recognition fast and efficient. They had a smartphone-only version too, but it had some limitations, if I recall, because the processing power just wasn't quite there yet.
Oh, and the QR codes were per student, so answers could be tracked.