--- - |2+ Background Sleep variables have been linked to improved functioning of learning and memory throughout life, with most studies focusing on older children and adults. Since infancy is a time of outstanding plasticity, sleep variables could be particularly important for cognitive development in that age group. Methods This is a longitudinal study collecting data from 40 infants at four different time points of 4, 6, 8 and 10 months. Sleep variables were assessed using actigraphy for a week, as well as a sleep questionnaire. Eye‐tracking was employed to examine developmental cognitive trajectories. Infants had to remember the location of a toy that had previously been linked to a sound and an eye‐tracker recorded whether they were searching the correct location upon hearing the sound. Results Based on their trajectories between 4 and 10 months, infants were divided into two groups who shifted their response strategies at different time points. Those two groups also differed in other aspects of their looking patterns and scored increasingly differently in the Ages & Stages Questionnaire over time. Time spent awake in the night early in life was reduced in the group who changed their strategy earlier. Conclusions While previous research examined the relation of infant sleep and cognitive functioning measured once, this paper provides first evidence that night wake time can serve as a marker for different cognitive trajectories. - Journal of Child Psychology and Psychiatry, EarlyView.