Learning and teaching complex cultural knowledge calls for meaningful participation in different kinds of symbolic practices, which in turn are supported by a wide range of external representations, as gestures, oral language, graphic representations, writing and many other systems designed to account for properties and relations on some 2- or 3-dimensional objects. Children start their apprenticeship of these symbolic practices very early in life. But being able to understand and use them in fluid and flexible ways poses serious challenges for learners and teachers across educational levels,...