Time needed: 10 – 20 min
Why? Drawing is a method nearly every child love to do that and to express their view at this world with this method. This method is forcing and support phantasy development and cross line connections and expression of absorbed knowledge in another language.
When? Every time you think your class need a relaxing of the teaching and learning atmosphere.
How? Some times it is very refreshing for children to have open topic and to fulfill tasks which are not pressed artificial in frames. Let them just draw things which are surrounding them, and you will surprisingly find out, that even a painting of a cup, will have very different results and if you are very careful as a teacher you can use those paintings also to learn about your children and start to understand about their different views of the world.
Any risks? Every child has different speeds to fulfill such a task, prepare for early finishers extra tasks.