While members of the same family are assumed to share similar mobility chances, this paper seeks to answer the following puzzle: why do only some children of the same family attain a level of education considered to be socially desirable whereas their siblings do not? The essence of an answer lies in the fact that the same parents could play rather dissimilar roles in the education of their different children. Using part of qualitative data collected in Hong Kong between 1996 and 1997, this paper focuses on what selective parents did for their children's education. The data illustrated that in deciding what they would and could do for each of their children's education, parents responded to their children's academic ability, resource availability, and ideology. The educational attainments of children of the same family could be very diverse not merely because of children's different academic performances but because of the deliberate decisions of their parents in formulating strategies for basic survival or for advancement. The same parents could be seen as enhancing the education of their sons and/or younger children at the expense of the education of their daughters and/or elder children. This suggests that mobility is of an interdependent nature and, in turn, leads me to argue that the mobility of members of the same family should be considered together and not in isolation, and to support the stance that the family, rather than an individual, should be the unit of analysis in mobility studies.