Fathers in Western countries allocate progressively more time to childcare. However, most research on how parental time inputs affect child development focuses on maternal time, and it remains empirically unclear how paternal involvement in the child’s upbringing influences child outcomes. This study provides the first systematic account of how father-child time (in total and across activity types) relates to children’s cognitive development, measured using the Peabody Picture Vocabulary Test. In addition, it examines whether and how paternal education moderates these associations. To accomplish this, the study uses unique, longitudinal, time-diary data from an Australian sample of children aged 4-8 years (Longitudinal Study of Australian Children; n=3,273 children/6,960 observations). Results show that the total amount of father-child time is associated with small improvements in children’s cognitive functioning, whereas the amount of father-child time in educational activities is associated with moderate-to-large improvements. Such associations are similar for highly and less-highly educated fathers.