In the PISA 2006 program Slovenian students exceeded the international average of scientifi c achievements, while in the fi eld of living systems performed below the national average. The purpose of our analysis was to determine in which areas of biology Slovenian students are weak and in which they are strong, and to determine their biological knowledge in comparison to 23 other European countries, which, by various criteria, are the most comparable to Slovenia and interesting for us. We analysed 24 tasks that tested the biological knowledge in PISA 2006. We found that student achievement in Slovenia wasn’t poor in any of the tested biological topics. There are two factors that can explain lower achievements resolving individual tasks: (1) Question type: Students poorly answered the open-constructed response questions that require independent formulation of coherent responses. They were more successful with complex multiple choice questions and multiple choice questions, where they had to choose the correct answer from several given suggestions; (2) Diffi culty: Students didn’t perform as well with higher cognitive level tasks which required using knowledge. This suggests that in the period when these students were receiving elementary education, their biology teaching focused on developing knowledge of biological content (knowledge of science) and competence explaining phenomena scientifi cally, while the development of other knowledge (knowledge about science) and the competence to draw evidence-based conclusions (using knowledge) was inadequate. It is therefore in the hands of all in Slovenia involved in biological education, especially teachers of biology, to give students more opportunities for problem-solving, rather than only focusing on content.