International Comparative Studies of Science Achievement from the Time Perspective: The Third International Mathematics and Science Study versus the International Assessment of Educational Progress

The key question in international comparative studies of educational achievement is whether results can be trusted. The answer is unknown unless what is measured at one point in time can be compared with measurement at some other point in time. Results from the Third International Mathematics and Science Study (TIMSS) in Slovenia can fortunately be compared with results from the International Assessment of Educational Progress (IAEP) collected in 1991. Although TIMSS sampling was grade-based and IAEP sampling was age-based, allowing for differences in sampling shows that Slovene children, as well as those from all other compared countries performed approximately at the same level at both points in time. Age-based comparison placed Slovenia's 13-year-olds much lower on the international rankings list than the TIMSS grade-based comparison. But taking samples based on age and comparing only 13-year-olds in both samples shows very little difference in the results of these two studies. Furthermore, achievement varies very similarly in both studies with variables such as time used for school at home, time spent watching television and the disposal of study aids. Despite the different approach used in each study, comparison of achievement between TIMSS and IAEP reveals exceptional similarity.