Behaviorism is the theory that human behavior can be measured, trained, and changed through conditioning techniques without reference to internal mental states. Key figures who developed behaviorism include Ivan Pavlov, known for classical conditioning experiments with dogs, and B.F. Skinner, who discovered operant conditioning through experiments rewarding pigeons with food. In behaviorism, learning is viewed as an objective process where behaviors are shaped through reinforcement or punishment. This theory influenced classroom practices where teachers reward students for desired behaviors like sitting quietly.