The aim of this study is to examine whether or not the positive and negative items in the Mathematical Self-Confidence Scale employed in TIMSS 2015 lead to wording effect. While examining whether the expression effect is present or not, analyzes were conducted both on the general sample and on a separate sample for female and male students. To this end, data of 5724 students from Turkey who participated in TIMSS 2015 were used. Six different measurement models were created in the analysis of data and tested with Confirmatory Factor Analysis. The study revealed that positive items have a higher mean than the negative ones. In addition, it was concluded that the bifactor models fit the data better compared to the traditional DFA model, in which the model where negative items were taken as a separate factor are those that best fit the data. This situation is verified both in the general sample and the subgroups of females and males. In conclusion, it is recommended that the scale items should be created carefully and whether the positive and negative items result in separate factors should be examined.