The study was designed to investigate the factors thought to be relevant in the attainment of maturity of moral judgement in educationally sub-normal children: those of age, intelligence, and family influence, the last being specifically concerned with social position, parental discipline and family relationships. Sex differences in the development of moral judgement wee also considered. The subjects were 50 pupils, aged 11 to 16, of a day special school for E.S.N. children and measures used were a test of moral judgement, the Wechsler Intelligence Scale for Children, attainment tests of reading and vocabulary, the Bane-Anthony Family Relations Test, a test of parental discipline, and a social class assessment. Results showed the general low level of moral maturity in E.S.N. children but the expected age trend was barely evident. Intelligence was found to be significantly related to the development of moral judgement in E.S.N. boys, particularly where there were verbal factor or when in terms of mental age; findings for the girls were either inconclusive or less pronounced. Some of the related aspects of intelligence were of the type which are influenced by social factors. Results of comparisons between moral judgement and tests of verbal attainment were mainly inconclusive. The differences between social classes in maturity of moral judgements of both boys and girls were positive though non-significant, but moral maturity was not related to size of family or to major involvements with particular members of the family. Sensitisation-type maternal discipline was found to be very highly related to the development of moral judgement in E.S.N. boys, and there was a high negative relationship between psychological-type discipline and development of moral judgement in girls