Abstract — Staff and students in the UK often dismiss MCQs (Multiple Choice Questions) as being associated with rote learning, but not understanding. However one of the biggest results ever published in education shows how mistaken this attitude is. The most important aspect of deep learning is probably being concerned with reasons rather than only with conclusions. If you want to test for knowledge of reasons then you can easily design MCQs to give the facts and ask about reasons. More interestingly, you can use MCQs that ask about facts to provoke learners to search for reasons. One method is to have students design MCQs (together with automatic feedback explaining why each response is right or wrong): the PeerWise software can organise this as an assignment in large classes. Another method is to use questions delivered by EVS (electronic voting systems) to catalyse peer discussion, even in huge classes. This talk will discuss some of the big educational results, and also psychological research that partially illuminates the mechanism. Supporting website for a SALT seminar presented by Steve Draper of Glasgow University at Swansea on 23rd November 2011.