The course clarifies the concept of behaviour modification and its historical evolution. The identification of the steps involved follows. It applies the clinical and experimental methods, scientific approach of methodological behaviourism: Classical conditioning, operant conditioning, cognitive-social learning, among others. Counter-conditioning, fatigue, incompatible stimuli, inhibitory and disinhibitory effect, and so on, are equally treated. It further considers specific practical illustrations of common behaviour problems in the school. Ethical issues involved are also considered.