Purpose: Cross-cultural comparisons based on ordinal Likert-type rating scales have been threatened by response style which is systematic tendencies to respond to items regardless of the item content. So, this study aimed to investigate the effect of extreme response style and acquisance response style on TIMSS 2015 data.

Method: The sample of this descriptive study included eighth grade students of the countries Japan, Korea, Taipei, Turkey, Oman and Jordan. Students’ responses to scale regarding value on mathematics were used. To examine the impact of response styles, partial credit model and partial credit model with response style were analyzed. Also, the estimates obtained from these models were compared

Findings: It was found that response styles existed in TIMSS 2015 data. Furthermore, the number of the students selecting the extreme categories were found to be lower than that of the students selecting relatively middle response categories. Additionally, item thresholds of the extreme categories were found to be distorted leading to biased determination of item response curves.

Implications forResearch and Practice: The presence of the response style in the large-scale assessment which guides policy makers in their regulations in the educational systems and gives information to teachers in their practices lead researchers to examine and control the effect of them.