The concept of moderate learning difficulties (MLD) is not clearly understood in its definition and in its general use. Nevertheless, as a distinct area of special educational needs (SEN) this category has constituted about a quarter of all of those pupils identified as having SEN in England. This paper reports the analysis of findings from an ongoing research project in an attempt to improve understanding of the MLD category. Pupils (aged 12-14?years) identified as having MLD were compared with others in the same classes identified as having either specific learning difficulties or low attainments in terms of literacy, reasoning and dispositional measures. The paper shows that the label of MLD is often used in an over-generalised way in schools and that although there are some differences in reasoning and literacy abilities between those identified as having MLD and those who have not, no such differences were found in learner self-concept and in pupils' attitudes to education and learning questioning the current definition of MLD which includes associated low self-esteem. Reasons for lack of clarity in the definition/category of MLD are discussed, as are implications for future use of the term.