This study offers curriculum developers, teachers, and science education researchers a fine-grained profile on strengths and weaknesses in specific science domains and topics. The study involved a representative sample of 3844 Norwegian pupils in grade 8. Their responses on 216 TIMSS items in 18 topics from 4 science domains were modelled in a hierarchical item response model. An internal comparison identified topics that were relatively harder or easier compared to other topics for Norwegian pupils, and an external comparison identified topics that were relatively harder or easier for the Norwegian pupils compared with the average of TIMSS participating countries. Interpretation of the profile necessitates contextualisation; hence, these strengths and weaknesses, as well as their plausible explanations and possible implications, are discussed from the perspectives of curriculum development, teacher training, and science education research.