In animals that experience interactions with conspecifics while young, social interactions appear to be a necessary prerequisite for typical behaviour. Eusocial insects have large colonies where individuals experience a large number of social interactions with nest mates during all life stages, making them excellent candidates for understanding the effects of social isolation on brain development and behaviour. Here, we used the honey bee Apis mellifera to study the effect of social isolation and group size on reward perception and discrimination learning and memory. We confined day--old adult workers into three different size groups (1, 8 or 32 bees) for 6 days during a critical period associated with adult behavioural maturation. We quantified their sucrose responsiveness, their ability to use and remember olfactory cues to discriminate between sucrose and salt (i.e. discrimination learning), and four biogenic amines in the brain. We found that the smaller the group size, the more responsive a worker was to the sucrose reward. Honey bees raised in groups of 32 performed the best in the learning trials and had the highest levels of dopamine. We found no effect of group size on memory. The observed group size effect on learning but not memory supports the hypothesis that social interactions modulate learning through the dopaminergic system.