In the learning theories of Skinner and Hull, the most fundamental operation is reward. Consider the problems to be faced in a school such as that discussed by Barton. This is a school in a medium-sized subnormality hospital in a large northern city, attended by children for whom places cannot be found in other schools for the educationally severely subnormal. Somewhat more subtle linguistic skills, as well as articulatory skills and object naming, are also susceptible to reward training. For normal children, waving goodbye is often a very early and popular form of social exchange, although greeting strangers by saying hello may sometimes be inhibited by shyness. The basic methods of behaviour modification are the giving of both tangible and social rewards systematically for small steps towards all kinds of skills, and the equally systematic withdrawal of reward for antisocial or disruptive behaviours.