Background: The presence of red appears to hamper adults' cognitive performance relative to other colours (see Elliot & Maier, 2014, "Ann. Rev. Psychol." 65, 95). Aims and sample: Here, we investigate whether colour affects cognitive performance in 8- and 9-year-olds. Method: Children completed a battery of tasks once in the presence of a coloured screen that was one of eight colours and once in the presence of a grey screen. Performance was assessed for each colour relative to the grey baseline, and differences across colours were compared. Results: We find a significant difference in performance across colours, with significantly worse performance in the presence of red than grey. The effect of colour did not significantly interact with task. Conclusion: The findings suggest that colour can affect children's cognitive performance and that there is a detrimental effect of red. Findings are related to the adult literature and implications for educational contexts are discussed.