Final answer:
The school of psychology that only studies what can be objectively observed is known as behaviorism, championed by psychologists like John Watson and B.F. Skinner, and is exemplified by Pavlov's classical conditioning experiments.
Step-by-step explanation:
The school of psychology that suggests psychologists should study only what can be objectively observed is known as behaviorism. This approach to psychology emerged early in the 20th century, led by figures such as John Watson and B.F. Skinner, who emphasized the importance of studying behaviors that can be seen and measured, rather than internal mental states. Behaviorism focused on learning through interactions with the environment, without considering the mind's internal mechanisms. Notable experiments, like those conducted by Ivan Pavlov with classical conditioning, exemplified this idea by demonstrating learning through observable stimuli and responses.