Time needed: 10-20 min
Why? Students learn how to compress absorbed knowledge to make is understandable in a short version for others.
When? This method can be used after a taught topic is finished.
How? Divide students in groups of two students, let them choose one for them interesting theme out of the taught topic. Give them the task to create a postcard for friends based on that chosen theme. Let them send it to their friends later on, or use the postcard to send in inside the class and the other groups have to explain what they understood about that postcard.
Any risks? This method also will need a lot of time, but those methods are good to let them go deeper inside the topics and create something by self. For the teachers it will be a good evaluation instrument what students really absorbed from the taught topic.