This article tries to understand and interpret the reasons behind the marked decline in the TIMSS Advanced physics achievement test for students taking advanced physics courses at secondary school level in Norway and Sweden. Since it is not easy to identify a single reason that might have caused this decline, an attempt is made to explore possible influences by examining in a systematic way, changes in all contextual and background variables, as well as their co-variations with achievement scores. The results presented here offer a comprehensive view of the situation, and it is argued that a lack of focus on the basic subject skills in the lower grades combined with poor mathematical prerequisites might be seen as the major factors behind the marked decline in physics achievements for the two countries.

Keywords: TIMSS Advanced, physics, trend data, accounting for decline