Background: There is growing evidence that children with motor difficulties are at risk of psychosocial problems and vice versa. However, it is not clear how far different aspects of motor function are predictive of psychosocial well-being in the context of other powerful factors, such as family upset, that are known to affect psychosocial development. Aims: To investigate the role of basic motor skills and primary reflex persistence in young children with severe emotional and behavioural difficulties (EBD). Sample: From a total sample of 225 children, three groups were selected: children excluded from school (severe EBD) (n = 29), a male comparison group (n = 38), and a female comparison group (n = 45). The groups were matched (at group level) on age, IQ, and level of social disadvantage. Method: All of the selected children completed a range of standardized motor, cognitive, social, and behavioural measures, as well as a clinical protocol for primary reflex persistence. Results: Children with severe EBD had significant levels of motor difficulties, primary reflex persistence, and family upset, as well as significant literacy problems, attention deficits, and raised levels of hyperactivity/impulsivity relative to the comparison groups. A hierarchical multiple regression analysis revealed that basic motor skills, primary reflex persistence, family upset, hyperactivity, and literacy were all significant predictors of psychosocial functioning. Conclusions: The findings suggest that motor difficulties and primary reflex persistence may act as independent stressors of psychosocial functioning in children with EBD. We suggest that specific movement interventions should be adopted to complement existing provision for children at risk of psychosocial problems.