Mysteries can be extremely engaging, powerful thinking skills activities. They involve giving small groups of learners a set of cards containing many different pieces of information and challenging them to answer a Focus Question by sorting, connecting and making sense of the information.
The mystery can be convergent (there is one right answer - like in this maths example: "Does Amelie make it to the catwalk?"), or divergent (there are a number of ways learners can connect the information and draw different conclusions - like in some of these History examples).
Mysteries present very important opportunities for meta-cognition (thinking about thinking), and sufficient time should be allowed for plenarising the activity and engaging learners in reflection about how they went about the task. Also encourage learners to consider where they can use these skills (sorting, classifying, evaluating information, drawing together evidence, making inferences, etc) more widely.
For examples in most KS3 subjects from the very useful Nottinghamshire County Council Thinking Skills site, click here.