Final answer:
The experience of not getting into desired classes after late registration acted as a negative reinforcer, encouraging on-time class registration in subsequent semesters.
Step-by-step explanation:
In the context of operant conditioning, the student's experience of registering late and not getting into desired classes last semester would serve as a negative reinforcer when considering subsequent on-time registration behavior. A negative reinforcer entails the removal of an aversive stimulus (in this case, the experience of being unable to enroll in preferred classes) to increase the likelihood of a certain behavior (registering on time). Since the prior experience led to increased on-time registration behavior, it facilitated a form of negative reinforcement.