Low socio-economic status is a recognised composite measure made up of income, education and occupational social class, which is a risk factor for poor physical and mental health and late life dementia. Here, we distinguish between components of childhood socioeconomic status to explore their separate influences of childhood and adult occupational social class (OSC), childhood mental ability and education on late life cognitive ability and change trajectories. Cognitive data were collected longitudinally from a sub-sample (N = 478) of the Aberdeen 1936 birth cohort tested on up to 5 occasions between ages 63 and 78 years. Age 11 mental ability scores were available for all participants. We used longitudinal multi-level linear modelling to explore models of cognitive change that distinguished between the possible influences of parental occupation, participants' own occupation as adults, duration of formal education, childhood mental ability and the participants' own occupation. We showed that parental occupation and the participants' own occupation are independently associated with cognition in late life, but do not influence the trajectory of cognitive change. However, when models include childhood mental ability and education the influence of parental and participant occupation is no longer significant. The association in these data between parental occupation and late life cognitive variation is accounted for by childhood mental ability and duration of formal education. However, we cannot exclude the possibility that parental occupation in early life influences early life mental ability and duration of education. The trajectory of change with age is similar across all models, with none of the life course factors (education, parental and participant occupational social class and childhood ability) significantly co-varying with the trajectory of cognitive variation. (C) 2016 Elsevier Ltd. All rights reserved.