In TIMSS 2003 Study knowledge was classified by three different cognitive domains (Mullis, Martin, Smith, 2003): factual knowledge, conceptual understanding and reasoning and analysis. Every domain was tested by different items (Martin, Mullis, Chrostowski, 2004).The outcomes of a comparative study carried out in Estonia and Germany in 1996 1999 showed that the Estonian students had very good declarative knowledge at the same time the German students being much more successful in applying their knowledge in computer-simulated tasks (Reiska, 1999). In TIMSS 2003 the Estonian 8th graders performed very well achieving the fifth result in science.Hypothesis Taking into account the outcomes of the comparative study with Germany we studied the Estonian 8th grade students' performances in different cognitive domains. We raise the following hypothesis:" the performances of the Estonian 8th grade students differ in different cognitive domains, being best in factual knowledge; " the students' performance in different cognitive domains depends on their SES; " science related resources (teacher qualifications, teachers' use of conceptual teaching strategies) influence students' achievement in different cognitive domains; Methodology To find out students' achievement in different cognitive domains we first grouped the items by cognitive domains. After that we defined three variables, one for each cognitive domains.Results Looking at students' achievement in the three cognitive domains, we find out that the achievement in reasoning and analysis (mean: 1,177) is significantly lower than in the two other domains (mean in conceptual understanding: 1,246; mean in factual knowledge: 1,253). We can say that the achievement of the Estonian students is somewhat dependent on the income per capita in their family. The students' achievement in all cognitive domains depends on their background and the highest education level of their parents. The highest dependence from the background can be seen in conceptual understanding. It is very important to underline that with the low background index the growth of achievement in all cognitive domains is higher than with the high background index. It shows that the most important leverage would be improving the situation of the students with the lowest background index.We can see no relationship whatsoever between the students' achievement and their teachers age. The students' achievement in the two other cognitive domains depends on their teachers' experience. The students' achievement also depends on their teachers' satisfaction with their work: the higher the satisfaction level, the higher the students' performance. We can see a clear relationship between the achievement and the level of teachers' formal education completed, especially with conceptual understanding and reasoning and analysis.Literature Mullis, I. V. S., Martin, M. O., Smith, T., A. (Eds.) (2003): TIMSS Assessment Frameworks and Specifications 2003 2nd Edition. International Study Center, Boston College. Martin, M. O., Mullis, I. V. S., & Chrostowski, S. J. (Eds.) (2004): TIMSS 2003 Technical Report. Chestnut Hill, MA: TIMSS & PIRLS International Study Center, Boston College.Reiska, P. (1999): Physiklernen und Handeln von Schülern in Estland und in Deutschland. Eine empirische Untersuchung zu zwei unterschiedlichen Unterrichtskonzepten im Bereich von Energie und Energieversorgung mit den Methoden Concept Mapping und Computersimulation. Frankfurt a. M.: Peter Lang.