Sweet, R. C., & Ringness, T. A. (1971). Variations in the intelligence test performance of referred boys of differing racial and socioeconomic backgrounds as a function of feedback or monetary reinforcement . Journal of School Psychology , 9 (4), 399–409. https://doi.org/10.1016/0022-4405(71)90031-8

Students were tested under either standardized conditions, receiving feedback concerning correct answers, or contingent monetary reinforcement for correct answers.

Two groups of students participated. The first consisted of 156 elementary school males between the ages of 6 and 13 who had been seen during the previous year by school psychologists. The second consisted of 48 students from the same classrooms who had not been referred to the school psychologist.

The verbal section of the Wechsler Intelligence Scale for Children was used as the dependent variable.

Middle-class white students did not differ in performance across conditions. Lower-class white students performed significantly better under the monetary reinforcement condition when compared to the feedback alone condition. They also performed significantly better under the feedback alone condition when compared to the standardized condition. The performance of lower-class African-American students did not differ across conditions. It was suggested that this was due to the fact that all examiners were white females (which was found to have an effect on test scores in an earlier study).