BACKGROUND: Eczema and asthma are common conditions in childhood that can influence children’s mental health. Despite this, little is known about how these conditions affect the well-being of children in school. This study examines whether symptoms of eczema or asthma are associated with poorer social and mental well-being in school as reported by children and their teachers at age 8 years. METHODS: Participants were from the Avon Longitudinal Study of Parents and Children. Measures of child well-being in school were child-reported (n = 6626) and teacher reported (n = 4366): children reported on their enjoyment of school and relationships with peers via a self-complete questionnaire; teachers reported child mental well-being using the Strengths and Difficulties Questionnaire [binary outcomes were high ‘internalizing’ (anxious/depressive) and ‘externalizing’ (oppositional/hyperactive) problems (high was >90th percentile)]. Child rash and wheeze status were maternally reported and symptoms categorised as: ‘none’; ‘early onset transient’ (infancy/preschool only); ‘persistent’ (infancy/preschool and at school age); and ‘late onset’ (school age only). RESULTS: Children with persistent (OR 1.29, 95% CI 1.02 to 1.63) and late onset (OR 1.48, 95% CI 1.02 to 2.14) rash were more likely to report being bullied, and children with persistent wheeze to feel left out (OR 1.42, 95% CI 1.10 to 1.84). Late onset rash was associated with high teacher-reported internalising behaviours (OR 1.61, 95% CI 1.02 to 2.54), and persistent rash with high externalising behaviours (OR 1.37, 95% CI 1.02 to 1.84). Child sleep and maternal mental health explained some of the associations with teacher-reported mental well-being. CONCLUSION: Symptoms of eczema or asthma can adversely affect a child’s social and mental well-being at primary school. This suggests interventions, such as additional support or education of peers, should begin at early stages in schooling.