Purpose Speech-language practitioners recognise the importance of metapragmatic (MP) ability (the ability to explicitly reflect on pragmatic rules) in therapy for children with pragmatic and social communication difficulties. There is inconclusive evidence in the literature regarding both the development of metapragmatic ability in children with typical language and the expected levels of explicitation (reflection on pragmatic behaviours) in children's metapragmatic descriptions. The main purposes of this study were to investigate the reliability of a novel task of metapragmatic awareness (the Assessment of Metapragmatics or AMP) and to investigate typical developmental trends of metapragmatic ability and metapragmatic explicitation using the AMP task. Main results Analysis of pooled data from 40 children with typical language development aged between six and eleven years and 48 children with communication impairments indicated that the AMP task had satisfactory internal consistency and inter-rater reliability. For children with typical language development, there was no relationship between gender and metapragmatic ability as measured by AMP. There was a linear relationship between age and AMP task scores and between age and explicitation. The scoring system used in the AMP task was sensitive to age-related changes in metapragmatic ability in a normative sample. The sophistication of metapragmatic awareness (explicitation) also increased with age. At age six years, children demonstrated metapragmatic awareness in their responses to 74% of AMP stimuli items; this increased to 95% of AMP items at ages 10–11 years. Conclusions The AMP is a reliable measure of development in MP explicitation for children with satisfactory face validity in terms of acceptability to communication professionals and to child participants. From age six, children have some awareness of pragmatic acts and can identify and relate linguistic cues or pragmatic rules in atypical interactions of the type depicted in the AMP. The AMP task solicited significantly increased frequency of use of higher levels of MP explication beyond seven years of age in children with typical language development. Learning outcomes: Readers will explain the development, reliability and structure of a novel task that measures the ability of a child to understand and explain pragmatic rules. Readers will also identify age related changes in this ability in a sample of typically developing child participants.