Willis, J., & Shibata, B. (1978). A comparison of tangible reinforcement and feedback effects on the WPPSI I.Q. scores of nursery school children . Education & Treatment of Children , 1 (2), 31–45. https://psycnet.apa.org/record/1980-06444-001

Also, accessible at web link: https://www.jstor.org/stable/42940487 ​

Students were tested under one of three conditions: (1) token reinforcement contingent on each correct response with the provision of back-up reinforcers (reinforcement condition), (2) token reinforcement contingent on correct responses without the provision of back-up reinforcers (feedback condition), and (3) standard conditions.

Participants included 30 preschool children (20 boys and 10 girls) ages 3 to 3 1/2, from lower socio-economic families in a small rural town in Ontario (Canada).

Performance on the Wechsler Preschool and Primary Scale of Intelligence (WPSSI), including Verbal, Performance, and Full-Scale scores, was used as the dependent variable. Students were also pre-tested using this test. Average pretest to retest interval was 16.3 days.

Feedback did not increase the number of correct responses. Tangible reinforcement did result in a marked, general increase in IQ scores. The reinforcement condition also resulted in more positive student attitudes toward the test.