Calculation depends on the majority of the abilities within the domain of general intelligence (Blair et al., 2005). Most major theories of intelligence include numeracy or quantitative thinking as one aspect of general cognitive skills (Kaufman et al., 2013). In Chapter 1 of this volume, O’Neill and Gillespie described an example of the cognitively complex social practice of sharing a cup of tea. This activity includes actions like buying tea, measuring the amount of water needed and using a machine to boil it, telephoning a friend’s number, and inviting him or her for a visit to a certain address at a certain time. An interesting aspect of this list of actions is that all the activities require using measurement systems or numbers. In fact, numbers and numerical cognition are embedded in our current society. Learning is a cognitively demanding activity and learning or relearning numeracy is particularly demanding. That is why numeracy is one of the key targets of basic education; and may explain the relative scarcity of attempts to rehabilitate mathematical cognition.