Research to measure the influence of family on academic and professional careers is mainly based on data on individuals and their ascendants. These data tend to reduce the influence of the family environment to the effect of characteristics measured in surveys, such as the qualifications and professions of each parent. The portion of variance explained by these variables provides a low, skewed estimate of the influence of family of origin, confined solely to these explanatory variables: it ignores the potential impact of unobserved or unobservable aspects. This article breaks through these limitations via the tradition of sibling models. It uses data on siblings available in two surveys: the Survey on Training and Professional Qualifications (FQP) by INSEE (2003) and the Survey on the Intellectual Level of School-Age Children, by INED (1965). Observing and modelling the career path of individuals that have experienced a similar family socialisation allows us to take due account of all forms of transmission common to brothers and sisters. Family influence is thus considered in the broad sense as the effect of the social-origin environment as a whole. As it leads to a resemblance between the career paths of siblings, we describe this influence as “cohesive”. The data from the FQP survey show that cohesive family influence explains half of the variability in educational levels between individuals, and one-third of the variability in professional levels. Within the portion relating to the cohesive family influence, only half is explained by the characteristics of the family environment observed in the survey. Additionally, the family influence is stronger for same-sex sibling pairs when the age difference between brothers and sisters is small or when the parents have homogenous qualifications.