The present study analyses the extent to which families' educational processes and parents' attitudes towards science explain social disparities in scientific competency. Three research questions were addressed: (1) Which profiles can be identified for families' educational processes and parents' attitudes towards science? (2) Do families' educational processes and attitudes towards science depend on social class? (3) How important are families' different profiles for children's development of scientific competency? Data is based on a representative sample of N=9577 German students in the 9th grade taken from PISA 2006. A Latent-Class-Analysis identified four types of families which differ in their profiles of educational processes and parents' attitudes towards science. The distribution of each of the four family types across the different social classes (EGP classes) varies from 9 to 40 percent. This argues against the assumption that homogenous attitudes and patterns of behaviour are specific to social classes. Regression analyses on the students' scientific competency showed specific effects for the family types as well as for the social classes. When controlling for social background of the students, the specific effects of the family types remain. The specific effects of families' educational processes and parents' attitudes towards science on students' scientific competency can be found largely independent of social class and they thus display a kind of horizontal disparity in the scientific competency of students.