Diagnostic multiple-choice questions have long been used to assess students’ understanding. However, not all diagnostic questions are created equally, and thinking does not need to stop once students have got the correct answer. In the Tips for Teachers guide to Diagnostic Questions , Craig Barton explores what makes a good diagnostic question and the best ways to gather student data live in the classroom. Then he considers innovative methods to use diagnostic questions beyond simply obtaining the correct answer, aiming to challenge students further and gain a more accurate sense of the depth of their understanding.