B.F. Skinner developed the theory of operant conditioning based on Thorndike's law of effect. Operant conditioning uses reinforcement and punishment to modify behavior. Reinforcement strengthens behaviors by providing rewards, while punishment weakens behaviors by introducing unpleasant consequences to reduce their likelihood in the future. Behavioral counselors apply techniques like reinforcement schedules, shaping, chaining, and generalization to help clients achieve therapeutic goals by changing their behaviors.