Early individual differences in executive functions (EFs) are predictive of a range of developmental outcomes. However, despite the importance of EFs, little is known about the processes underlying these early individual differences. Therefore, we investigated the association between 14-month-old infants’ attention on a reaching version of the A-not-B task and task success. We hypothesized that both strategic focused attention (measured as percentage looking time towards the correct location during delay) and attentional flexibility (measured as number of looks per second to available stimuli during delay) would relate positively to task performance. Infants performed the A-not-B task wearing a head-mounted eye tracker (N = 24). Results were trial-dependent and partially supported the hypotheses: (1) infants who were better able to flexibly shift attention between available stimuli on the first pre-switch trial showed better task performance overall; and (2) strategic focused attention to the hiding location during the first switch trial was positively related to performance on that particular trial only (trend-level effect). Thus, the study shows preliminary evidence that particularly attentional flexibility is a key factor underlying EF performance in young children. Advantages and challenges of working with head-mounted eye tracking in infants are discussed.