Examining the effect of instructional clarity and attitude on science achievement in eighth grade TIMSS applications

The purpose of this study is to compare the effects of instructional clarity and attitude on science achievement of eighth grade students from Türkiye who participated in TIMSS 2015 and TIMSS 2019. Within the scope of the study, the effects of liking science, confidence in science and valuing science sub-dimensions of attitude on achievement were examined. After item response theory analyses using common items between the applications, ability estimates were obtained and then structural equation model analyses were performed. The findings of the study revealed that science achievement and science self-confidence scores increased statistically significantly in the 2019 implementation compared to the 2015 implementation. Structural equation model analyses revealed that the variables of liking science and valuing science had a negative effect on science achievement in both 2015 and 2019 implementations, while self-confidence in science and instructional clarity had a positive effect on science achievement. It is thought that the negative effect of liking science and valuing science on science achievement is due to the effect of parents on students' affective characteristics. This study is considered important in terms of providing the opportunity to monitor the effect of affective variables on achievement. Keywords: science achievement, instructional clarity, TIMSS, attitude, structural equation modeling.