In 1913, John B. Watson, the American psychologist, pointed out that human learning could be studied like Ivan Pavlov’s dogs. That’s the start of behaviorism.
Behaviorism belongs to science of psychology. It focuses on human’s measurable behaviors and see how those behaviors determine or effect their further actions. For example, by rewarding some behaviors and punishing for others, young children can learn how to behave themselves. There’s even thoughts that with appropriate condition, people can turn young children in any type of expected person.
This theory dominated the science of psychology for half a century until 1960s. People started to realize that thoughts inside our heads cannot be measured, so the behavior would be hard to predict or determine. Also, evolutionary psychology made people think about the inheritance of intelligence and personality, and could hardly be learned.
Although behaviorism is no longer a dominant force in psychology, the findings of theory are still widely applied, especially in education and therapy. When you buy your child a toy because he or she achieved a goal, you are using it.