Charlie's operation is experimental, and in order for the doctors to be sure they have the best possible subject for the experiment, they must find out all they can about their candidates, and evaluate and compare their various attributes. Also, by having the results of the tests taken before the operation by their chosen subject, the doctors will have a basis for comparison in order to measure the effects of the procedure once it is done.
Charlie must take a battery of tests "so they will see if they can use (him)" (March 3). These tests include the Rorschach, or "inkblot" test and the Thematic Apperception Test, both of which evaluate the level of Charlie's personality development. Charlie must also perform tasks involving puzzles and mazes, which measure his intelligence quotient, or IQ.
Based on the results of his tests, Charlie is actually not the perfect candidate for the operation, but he is chosen because he is "the best one they testid", and because of the unusually strong degree of motivation which he shows. It is not often that a person with his level of intelligence has such a strong drive to improve himself, and for this reason, the doctors, along with Miss Kinnian, the teacher at the Center for Retarded Adults, decide to go ahead and use him in the experiment. After the operation has been completed, they are able to measure Charlie's progress by having him take the tests again, and by comparing the results. In this way, the doctors are able to use concrete statistical data in monitoring what is happening to Charlie, and in evaluating the effectiveness of the experiment.
The reason he had to take a test before his operation was to see if there would be any change n the way he responds to questions.