Two Colleagues Are Debating Over Whether Giving Extrinsic, Arbitrary Rewards

Two colleagues are debating over whether giving extrinsic, arbitrary rewards like candy or giving intrinsic rewards like gaining new skills and passing to new material are better ways of motivating children to study. They agree to the following study, using a 6th grader who, with his parent's approval, has volunteered to help: First, no rewards are given for studying. Next an extrinsic reward candy) is given, then no reward, then the extrinsic reward of candy is given again, then a combination of candy and pointing out how much the child has learned. Next a return to extrinsic reward only. On another series of days the child is first given no reward, then a period of only pointing out how much has been learned. Next, no reward is given followed by again pointing out how much is learned. The both rewards are presented together, and finally there is a return to just pointing out how much is learned. In each of these many phases, the child's teacher keeps track of the speed of his progression through his required work. What single-case research design are these colleagues using?

A) A-B-A design
B) interaction design
C) multiple baseline design
D) changing criterion design