These days we are keen to make the most of our test data, particularly when it comes to informing next steps for teaching and learning. Sometimes we may examine how students have responded to particular questions on a test. This is good practice. It can be very enlightening to see what students found difficult (or easy) within a particular assessment and to think about the responses they made. It is also always important to know what was actually tested and how this matches our learning intentions. However, we must take care when dealing with responses to single questions. Making judgements as to what an individual knows (or doesn’t know) on the basis of a response to a single question is problematic and can lead to poor decision making.