People with PWS frequently present with an apparently advanced level of vocabulary and conversational skills and thereby appear cognitively very able. Whilst this aspect of the development of people with PWS can be very positive, it can also have the significant disadvantage of raising expectations to a level that then results in high degrees of stress and failure. The anecdotes we give in this chapter help to illustrate this point as the particular problems or skills the anecdotes illustrate are not easily captured in a meaningful way through just reporting test scores. The rigidity of thinking of people with PWS and their inability to generalise can be very disabling, and can be associated with behaviour that can put the person at risk. For example, one mother of a daughter with PWS interviewed as part of the Cambridge study described how she had attempted to teach her daughter not to speak to strangers. The daughter could repeat the instructions and warnings she had been given and appeared to have understood, but the next day the mother found her daughter in their front garden accosting passers by with the question ‘Are you a stranger?’ Another much more common observation of this type was the teaching of kerb drill.