An ABA practitioner observes behavior in the natural environment (classroom, home, public places etc.), to identify why the behavior occurs (known as antecedent) and what happens after the behavior (known as consequence). They also analyze what are the environmental factors that are responsible for a behavior to occur OR prevent certain behaviors from occurring. A consequence is the result that happens after the behavior. If the behavior is a desired behavior a reinforcer is introduced as a consequence for the behavior to reoccur. The key for effective intervention is to identify problem behaviors which need to be changed and which reinforers are acting for reoccurrence of behavior.