A behaviour rating scale intended primarily for use with mentally retarded children is described that is based on the behavioural descriptions of such children given by Pevsner (1963). A factor analysis showed that these descriptions could be viewed as being representable by two independent factors. The first of these factors, the AD factor may be seen to relate to attention/distractibility aspects of behaviour and shows a reliable correlation with verbal age and verbal quotient as assessed by the English Picture Vocabulary Test (EPVT), such that low EPVT scores predict greater distractibility. The second factor, the inhibition/excitation (IE) factor, did not correlate significantly with verbal age or verbal quotient but has, in other studies, shown relationships with style of social interaction and may be interpreted as relating to aspects of temperament. It is concluded that individual differences in the classroom behaviour of mentally retarded children may not be qualitatively different from those in non‐retarded children and that the scale described is a useful instrument for measuring these individual differences.