In this study, the effects of rewards on same-different judgments of size, color, and weight were investigated. Subjects were 45 children at the kindergarten and first-grade level. The children were assigned to one of three conditions: (1) rewarded for reporting black in the identification of the colors of balls contained inside gray jars, (2) rewarded for reporting white in the same task, or (3) not rewarded. Subjects were then required to respond "Same" or "Different" in size judgments of black, white, and gray discs presented for comparisons. Same-different judgments of the weights of black, white, and gray jars were also investigated. Results indicated that reward training did not differentially affect the same-different judgments of sizes or weights. However, differences in the mean discriminability of experimental groups and a suggestion of a contrast effect were demonstrated. Results and methodological changes in investigations of motivational factors on judgment are discussed. (Author/SB)