The use of the moderate learning difficulties (MLD) in the UK reflects much of what is loosely defined and lacking in clarity in the system of additional and different provision for children with difficulties and disabilities. D. Crowther et al. had to grapple in this research with the complexity of the MLD reference. MLD's determining characteristic was defined in terms of milder or more severe a difficulty that is learning progress in relation to the National Curriculum. The validity of educational categories is about whether categories have implications for additional or different educational provision or interventions for those with MLD compared to those without MLD. The broad and diverse MLD group has occupied a place along the continua of intellectual and social functioning and curriculum attainments between the severe learning difficulties and low attainers groups. For parents, having MLD identity is to distinguish their child from children with even lower attainments, and cognitive abilities with more organically based impairments.