B.F. Skinner, was born Burrhus Frederic Skinner in Susquehanna, Pa., on March 20, 1904. His interest in psychology rose while at Harvard University. Skinner was inspired by Bertrand Russell's articles on behaviorism. Also, Skinner was deeply influenced by the ideas of Francis Bacon. In 1931 he received a Ph.D. from Harvard and then continued to do research there until 1936. While there he developed the Skinner box. In 1936, Skinner joined the faculty of the University of Minnesota in Minneapolis, where he wrote 'The Behavior of Organisms' in 1938. From 1945 to 1948 he was a professor of psychology at Indiana University in Bloomington. During this period Skinner wrote an article discussing his air crib--a large, soundproof, germfree, air-conditioned box designed to provide an optimal environment for the first two years of a child's life. B. F. Skinner was a humanist, philosopher, and the foremost behavioral scientist of the 20th century. He discovered how immediate reinforcement determines future behavior through its relation to individual actions. He originated “shaping,” a technique of producing new behavior by immediately reinforcing small steps. In Walden Two, and Beyond Freedom and Dignity, Skinner argued that behavioral science was essential for improving the human condition. In the 21st century, shaping has become the standard for humanely and effectively improving behavior. Markle, S. (1969). Good Frames and Bad (2nd ed.). New York: Wiley.
The theory of B.F. Skinner is based upon the idea that learning is a function of change in overt behavior. Changes in behavior are the result of an individual's response to events (stimuli) that occur in the environment. A response produces a consequence such as defining a word, hitting a ball, or solving a math problem. When a particular Stimulus-Response (S-R) pattern is reinforced (rewarded), the individual is conditioned to respond. The distinctive characteristic of operant conditioning relative to previous forms of behaviorism (e.g., connectionism, drive reduction) is that the organism can emit responses instead of only eliciting response due to an external stimulus.
Reinforcement is the key element in Skinner's S-R theory. A reinforcer is anything that strengthens the desired response. It could be verbal praise, a good grade or a feeling of increased accomplishment or satisfaction. The theory also covers negative reinforces -- any stimulus that results in the increased frequency of a response when it is withdrawn (different from adversive stimuli -- punishment -- which result in reduced responses). A great deal of attention was given to schedules of reinforcement (e.g. interval versus ratio) and their effects on establishing and maintaining behavior.
One of the distinctive aspects of Skinner's theory is that it attempted to provide behavioral explanations for a broad range of cognitive phenomena. For example, Skinner explained drive (motivation) in terms of deprivation and reinforcement schedules. Skinner (1957) tried to account for verbal learning and language within the operant conditioning paradigm, although this effort was strongly rejected by linguists and psycholinguists. Skinner (1971) deals with the issue of free will and social control.
Skinner showed how positive reinforcement worked by placing a hungry rat in his Skinner box. The box contained a lever in the side and as the rat moved about the box it would accidentally knock the lever. Immediately it did so a food pellet would drop into a container next to the lever. The rats quickly learned to go straight to the lever after a few times of being put in the box. The consequence of receiving food if they pressed the lever ensured that they would repeat the action again and again.

Positive reinforcement strengthens a behavior by providing a consequence an individual finds rewarding. For example, if your teacher gives you £5 each time you complete your homework (i.e. a reward) you are more likely to repeat