Research with adults indicates that writing causal-explanatory and emotionally disclosing narratives of stressful experiences is related to psychological well-being. Limited research with children has shown mixed results, but developmental theory suggests that simple extrapolation from adult findings might be problematic. In this study, 9- to 13-year-old children engaged in three days of writing under emotional and non-emotional instructions, and completed measures of depression, anxiety, strengths and difficulties, and somatic symptoms both at baseline and 2 months following intervention. Narratives were coded using a developmentally appropriate, exhaustive coding system. Children in the emotional writing group wrote more about negative evaluations, problems, emotions, explanations and coping than children in the non-emotional writing group. However, those children who wrote more about negative evaluations, problems and explanations subsequently showed higher levels of anxiety, depression and difficulties. Due to limited narrative and emotional regulation skills, expressive writing may not benefit, and may even be detrimental for, some children.