Students’ academic achievement is related to different family background factors such as socio-economic, cultural, social, and cognitive factors. Research on family background has mainly focused on socio-economic factors, often neglecting the significance of providing a cognitively activating home environment. As a supplement to a largescale study assessing the competency of ninth-graders in Biology in Germany, 543 parents provided information on their socio-economic, cultural, and social background and worked on a domain-specific competency test. By means of hierarchical regression analyses, we established the separate and combined effects of the different background variables on students’ performance. Including all predictors simultaneously in a prediction model, only two — the number of books in home (β=.11) and the biology competency of parents (β = .26) — significantly predicted differences in their children’s competency in biology. Based on the results, we advocate a more comprehensive assessment of family background.